java集合--千锋教育

程序员文章站 2024-01-28 17:06:46

...

集合

一、集合概念

概念：对象的容器，定义了对多个对象进行操作的常用方法可实现数组的功能
和数组的区别：
- 数组长度固定集合不固定
- 数组可以存储基本类型和引用类型集合只能存放引用类型

Collection体系

java集合--千锋教育

父接口

特点：代表一组任意类型的对象，无序、无下标、不能重复
方法：
- boolean add(Object obj） //添加一个对象
- boolean addAll(Collection c)//将一个集合中的所有对象添加到此集合中
- void clear()//清空此集合中的所有对象
- boolean contains(Object o)//检查此集合是否包含o对象
- boolean equals(Object o)//判断此对象是否与指定对象相等
- boolean isEmpty()//判断此集合是否为空
- boolean remove (Object o) //在此集合中移除o对象
- int size()//返回此集合中的元素个数
- Object[] toArray()//将此集合转为数组
- Iterator iterator()//迭代

package Collection;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

public class Demo01 {
    public static void main(String[] args) {
        Collection collection =new ArrayList();
        //添加元素
        collection.add("香蕉");
        collection.add("橘子");
        collection.add("火龙果");
        //打印集合元素及个数
        System.out.println("元素个数为:"+collection.size());
        System.out.println(collection);
        //遍历
        //1.增强for  Collection不能使用下标
        System.out.println("====================");
        for(Object object:collection){
            System.out.println(object);
        }
        //2.迭代器  专门用来遍历集合
        System.out.println("======迭代器=======");
        Iterator it =collection.iterator();
        while(it.hasNext()){//hasNext()判断下一个元素是否存在
            String str = (String)it.next();//next()返回下一个元素
            System.out.println(str);
            //collection.remove(str);//遍历时不能用remove方法移除
            //it.remove();//可用迭代器remove移除

        }
        //判断
        System.out.println(collection.isEmpty());
        System.out.println(collection.contains("西瓜"));
        //移除元素
        collection.remove("橘子");
        System.out.println("元素个数为:"+collection.size());
        System.out.println(collection);
        //清空
        collection.clear();
        System.out.println("元素个数为:"+collection.size());
        System.out.println(collection);
    }
}
元素个数为:3
[香蕉, 橘子, 火龙果]
====================
香蕉
橘子
火龙果
======迭代器=======
香蕉
橘子
火龙果
false
false
元素个数为:2
[香蕉, 火龙果]
元素个数为:0
[]

package Collection;

public class Student {
    private String name;
    private int age;

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

package Collection;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

public class Demo02 {
    public static void main(String[] args) {
        //新建Collection对象
        Collection collection = new ArrayList();
        Student s1 = new Student("陈壹",21);
        Student s2 = new Student("陈贰",22);
        Student s3 = new Student("陈叁",21);
        //添加数据
        collection.add(s1);
        collection.add(s2);
        collection.add(s3);
        collection.add(s3);
        System.out.println("元素个数为:"+collection.size());
        System.out.println(collection.toString());
        //删除
        //collection.remove(new Student("陈壹",21));new 对象不会删除原来列表
        collection.remove(s3);//没有移除全部s3 删除一个

        System.out.println("元素个数为:"+collection.size());
        System.out.println(collection.toString());
        //遍历
        //1.增强for
        for(Object object : collection){
            Student s = (Student)object;
            System.out.println(s.toString());
        }
        //2.迭代器
        Iterator iterator= collection.iterator();
        while(iterator.hasNext()){
            Student s = (Student)iterator.next();
            iterator.remove();
            System.out.println(s.toString());
        }
        System.out.println(collection.toString());//remove 删除完毕
        //判断
        System.out.println(collection.contains(s1));
        System.out.println(collection.isEmpty());
    }
}
元素个数为:4
[Student{name='陈壹', age=21}, Student{name='陈贰', age=22}, Student{name='陈叁', age=21}, Student{name='陈叁', age=21}]
元素个数为:3
[Student{name='陈壹', age=21}, Student{name='陈贰', age=22}, Student{name='陈叁', age=21}]
Student{name='陈壹', age=21}
Student{name='陈贰', age=22}
Student{name='陈叁', age=21}
Student{name='陈壹', age=21}
Student{name='陈贰', age=22}
Student{name='陈叁', age=21}
[]
false
true

List

特点：有序有下表元素可以重复
方法
- void add(int index , Object o)//在index处插入对象o
- boolean addAll(int index,Collection c)//将一个集合中的元素添加到index处
- Object get(int index)//返回集合中指定位置的元素
- LIst subList (int fromIndex ,int toIndex)//返回fromIndex 到toIndex的元素

package List;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;

public class List01 {
    public static void main(String[] args) {
        //创建集合
        List list =new ArrayList<>();
        //1.添加元素
        list.add("小米");
        list.add("三星");
        list.add("苹果");
        list.add("华为");
        System.out.println("元素个数为:"+list.size());
        System.out.println(list.toString());
        //2.删除元素
        //list.remove("三星");
        list.remove(0);
        System.out.println("元素个数为:"+list.size());
        System.out.println(list.toString());
        //3.遍历
        //1.for循环
        System.out.println("=========1.for=========");
        for (int i = 0; i < list.size(); i++) {
            System.out.println(list.get(i));
        }
        //2.增强for
        System.out.println("==========增强for=====");
        for (Object object: list){
            System.out.println(object);
        }
        //迭代器
        System.out.println("==========迭代器======");
        Iterator it=list.iterator();
        while (it.hasNext()){
            String s = (String)it.next();
            System.out.println(s.toString());
        }
        //list迭代器 可以前向 后向 遍历 可以增改
        System.out.println("=========list迭代器======");
        ListIterator lit =list.listIterator();
        System.out.println("=====从前往后========");
        while(lit.hasNext()){
            System.out.println(lit.nextIndex()+":"+lit.next());
        }
        System.out.println("======从后往前====");
        while(lit.hasPrevious()){
            System.out.println(lit.previousIndex()+":"+lit.previous());

        }
    }
}
元素个数为:4
[小米, 三星, 苹果, 华为]
元素个数为:3
[三星, 苹果, 华为]
=========1.for=========
三星
苹果
华为
==========增强for=====
三星
苹果
华为
==========迭代器======
三星
苹果
华为
=========list迭代器======
=====从前往后========
0:三星
1:苹果
2:华为
======从后往前====
2:华为
1:苹果
0:三星

package List;

import java.util.ArrayList;
import java.util.List;

public class  List02 {
    public static void main(String[] args) {
        List list =new ArrayList<>();
        //添加数字
        list.add(10);
        list.add(20);
        list.add(30);
        list.add(40);
        list.add(50);
        list.add(60);
        list.add(70);
        System.out.println("列表元素为:"+list.size());
        System.out.println(list.toString());
        //删除元素
        list.remove(6);
        System.out.println("列表元素为:"+list.size());
        System.out.println(list.toString());
        //通过元素值移除元素 二种方法
        list.remove((Object)60);
        System.out.println("列表元素为:"+list.size());
        System.out.println(list.toString());
        list.remove(new Integer(50));//Collection类中 Student 不能通过new Student 删除 为什么？？？？  因为 对equals定义不同 Student 是通过地址判断 需重写成判断name age 才可以这样删除
        System.out.println("列表元素为:"+list.size());
        System.out.println(list.toString());
        //补充  subList  含头不含尾
        System.out.println(list.subList(1,3));

    }
}
列表元素为:7
[10, 20, 30, 40, 50, 60, 70]
列表元素为:6
[10, 20, 30, 40, 50, 60]
列表元素为:5
[10, 20, 30, 40, 50]
列表元素为:4
[10, 20, 30, 40]
[20, 30]

List 实现类

ArrayList:
- 数组结构实现查询快增删慢
- 运行效率快线程不安全
Vector(了解):
- 数组结构实现查询快增删慢
- 运行效率慢线程安全
LinkedList:
- 链表结构实现增删快查询慢

Arraylist: 储存结构-- 数组

package Collection;

import java.util.Objects;

public class Student {
    private String name;
    private int age;

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    @Override
    /*public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Student student = (Student) o;
        return age == student.age &&
                Objects.equals(name, student.name);

     */
    public boolean equals(Object o) {
        if(this==o){
            return true;
        }
        if(this==null){
            return false;
        }
        if(o instanceof  Student){
            Student s = (Student)o;
            if (this.name.equals(s.getName()) && this.age==s.getAge()){
                return true;
            }
        }
        return  false;
    }
}

package Arraylist;

import Collection.Student;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;

public class Demo01 {
    public static void main(String[] args) {
        ///创建集合
        ArrayList<Object> arrayList = new ArrayList<>();
        //添加元素
        Student s1 = new Student("刘德华",59);
        Student s2 = new Student("郭富城",55);
        Student s3 = new Student("黎明",54);
        Student s4 = new Student("张学友",59);
        arrayList.add(s1);
        arrayList.add(s2);
        arrayList.add(s3);
        arrayList.add(s4);
        arrayList.add(s4);
        System.out.println("元素个数为:"+arrayList.size());
        System.out.println(arrayList.toString());
        //删除元素
        arrayList.remove(new Student("张学友",59));//重写equals方法  可以删除
        System.out.println("元素个数为:"+arrayList.size());
        System.out.println(arrayList.toString());
        //遍历元素
        //1.增强for
        System.out.println("==========增强for===========");
        for (Object object:arrayList) {
            Student s =(Student)object;
            System.out.println(s.toString());
        }
        //2.下标 for
        System.out.println("========普通for==============");
        for (int i = 0; i < arrayList.size(); i++) {
            System.out.println(arrayList.get(i));
        }
        //3.迭代器
        // Iterator 迭代器
        System.out.println("==============Iteraor迭代器===========");
        Iterator it =arrayList.iterator();
        while(it.hasNext()){
            Student s =(Student)it.next();
            System.out.println(s.toString());
        }
        //ListIterator 迭代器
        System.out.println("==============ListIterator 前向迭代器===========");
        ListIterator lit = arrayList.listIterator();
        while(lit.hasNext()){
            Student s =(Student)lit.next();
            System.out.println(s.toString());
        }
        System.out.println("==============ListIterator 后向迭代器===========");
        while(lit.hasPrevious()){
            Student s =(Student)lit.previous();
            System.out.println(s.toString());
        }
        //判断
        System.out.println(arrayList.contains(s1));
        System.out.println(arrayList.contains(new Student("郭富城",55)));//重写 equals

    }
}
元素个数为:5
[Student{name='刘德华', age=59}, Student{name='郭富城', age=55}, Student{name='黎明', age=54}, Student{name='张学友', age=59}, Student{name='张学友', age=59}]
元素个数为:4
[Student{name='刘德华', age=59}, Student{name='郭富城', age=55}, Student{name='黎明', age=54}, Student{name='张学友', age=59}]
==========增强for===========
Student{name='刘德华', age=59}
Student{name='郭富城', age=55}
Student{name='黎明', age=54}
Student{name='张学友', age=59}
========普通for==============
Student{name='刘德华', age=59}
Student{name='郭富城', age=55}
Student{name='黎明', age=54}
Student{name='张学友', age=59}
==============Iteraor迭代器===========
Student{name='刘德华', age=59}
Student{name='郭富城', age=55}
Student{name='黎明', age=54}
Student{name='张学友', age=59}
==============ListIterator 前向迭代器===========
Student{name='刘德华', age=59}
Student{name='郭富城', age=55}
Student{name='黎明', age=54}
Student{name='张学友', age=59}
==============ListIterator 后向迭代器===========
Student{name='张学友', age=59}
Student{name='黎明', age=54}
Student{name='郭富城', age=55}
Student{name='刘德华', age=59}
true
true

源码分析

默认容量： DEFAULT_CAPACITY = 10 注意：如果没有向集合中添加元素默认为0 添加任意元素则为10 到达极限是扩容为原来的1.5倍

存放元素的数组 elementData

实际元素个数 size

add()方法：

源码

public boolean add(E e) {
    ensureCapacityInternal(size + 1);  // Increments modCount!!
    elementData[size++] = e;
    return true;
}

private static int calculateCapacity(Object[] elementData, int minCapacity) {
        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
            return Math.max(DEFAULT_CAPACITY, minCapacity);
        }
        return minCapacity;
    }

    private void ensureCapacityInternal(int minCapacity) {
        ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
    }
    private void ensureExplicitCapacity(int minCapacity) {
        modCount++;

        // overflow-conscious code
        if (minCapacity - elementData.length > 0)
            grow(minCapacity);
    }

private void grow(int minCapacity) {
        // overflow-conscious code
        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        if (newCapacity - MAX_ARRAY_SIZE > 0)
            newCapacity = hugeCapacity(minCapacity);
        // minCapacity is usually close to size, so this is a win:
        elementData = Arrays.copyOf(elementData, newCapacity);
    }

Vector: 数组

package Vector;

import java.util.Enumeration;
import java.util.Vector;

public class Demo0 {
    public static void main(String[] args) {
        //创建集合
        Vector<Object> vector = new Vector<>();
        //添加元素
        vector.add("香蕉");
        vector.add("橘子");
        vector.add("芒果");
        vector.add("西瓜");
        System.out.println("元素个数为:"+vector.size());
        System.out.println(vector.toString());
        //遍历元素  枚举法  增强for等也可以
        Enumeration elements = vector.elements();
        while(elements.hasMoreElements()){
            String s = (String) elements.nextElement();
            System.out.println(s);
        }
        //判断
        System.out.println(vector.contains("西瓜"));
        System.out.println(vector.isEmpty());
        //其他方法
        System.out.println(vector.firstElement());
        System.out.println(vector.lastElement());
        System.out.println(vector.elementAt(0));
        //删除元素
        vector.remove(0);
        System.out.println(vector.toString());
        vector.remove("西瓜");
        System.out.println(vector.toString());
        vector.clear();
        System.out.println(vector.toString());

    }
}
元素个数为:4
[香蕉, 橘子, 芒果, 西瓜]
香蕉
橘子
芒果
西瓜
true
false
香蕉
西瓜
香蕉
[橘子, 芒果, 西瓜]
[橘子, 芒果]
[]

LinkedList:

package LinkerList;

import Collection.Student;

import java.util.Iterator;
import java.util.LinkedList;
import java.util.ListIterator;

public class Demo00 {
    public static void main(String[] args) {
        //创建集合
        LinkedList linkedlist = new LinkedList<>();
        //添加元素
        Student s1 = new Student("刘德华",59);
        Student s2 = new Student("郭富城",55);
        Student s3 = new Student("黎明",54);
        Student s4 = new Student("张学友",59);
        linkedlist.add(s1);
        linkedlist.add(s2);
        linkedlist.add(s3);
        linkedlist.add(s4);
        System.out.println("元素个数:"+linkedlist.size());
        System.out.println(linkedlist.toString());
        //遍历
        //2.1for
        System.out.println("=========for============");
        for (int i = 0; i < linkedlist.size(); i++) {
            System.out.println(linkedlist.get(i));
        }
        //2.2增强for
        System.out.println("=======增强for============");
        for (Object obj : linkedlist){
            Student s =(Student) obj;
            System.out.println(s.toString());
        }
        //2.3迭代器
        System.out.println("==========迭代器==========");
        Iterator it = linkedlist.iterator();
        while(it.hasNext()){
            Student s =(Student)it.next();
            System.out.println(s.toString());
        }
        //2.4LiseIterator 迭代器
        System.out.println("========LiseIterator 迭代器=============");
        ListIterator lit = linkedlist.listIterator();
        while(lit.hasNext()) {
            Student s = (Student) lit.next();
            System.out.println(s.toString());
        }
        //判断
        System.out.println(linkedlist.contains(s1));
        System.out.println(linkedlist.isEmpty());
        //获取
        linkedlist.get(0);
        //删除
        linkedlist.remove(0);
        System.out.println(linkedlist.toString());
        linkedlist.remove(new Student("郭富城",55));
        System.out.println(linkedlist.toString());
        linkedlist.clear();
        System.out.println(linkedlist.toString());
    }
}
元素个数:4
[Student{name='刘德华', age=59}, Student{name='郭富城', age=55}, Student{name='黎明', age=54}, Student{name='张学友', age=59}]
=========for============
Student{name='刘德华', age=59}
Student{name='郭富城', age=55}
Student{name='黎明', age=54}
Student{name='张学友', age=59}
=======增强for============
Student{name='刘德华', age=59}
Student{name='郭富城', age=55}
Student{name='黎明', age=54}
Student{name='张学友', age=59}
==========迭代器==========
Student{name='刘德华', age=59}
Student{name='郭富城', age=55}
Student{name='黎明', age=54}
Student{name='张学友', age=59}
========LiseIterator 迭代器=============
Student{name='刘德华', age=59}
Student{name='郭富城', age=55}
Student{name='黎明', age=54}
Student{name='张学友', age=59}
true
false
[Student{name='郭富城', age=55}, Student{name='黎明', age=54}, Student{name='张学友', age=59}]
[Student{name='黎明', age=54}, Student{name='张学友', age=59}]
[]

java集合--千锋教育

泛型参数化类型

<T。。。>类型占位符表示一种引用类型

好处
- 提高代码的重用性
- 防止类型转换异常，提高代码安全性

泛型类

语法：类名后加<T,E,K…> T类型占位符是一种引用类型可以编写多个

package Mygeneric;

public class Mygeneric<T> {
    //使用泛型
    //1.创建变量
    T t;
    //2.方法参数
    public  void  show(T t){
        // T t =new T();  不可new对象  因为无法确定T的类型
        this.t = t;
        System.out.println(t);

    }
    //3.泛型作为方法的返回值
    public T getT(){
        return  t;
    }
}

package Mygeneric;

import com.sun.org.glassfish.external.amx.AMX;

public class TestGeneric {
    public static void main(String[] args) {
        //泛型为引用类型  不同泛型类型之间不能相互赋值
        Mygeneric<String> mg1 = new Mygeneric<String>();
        mg1.show("生活");
        System.out.println(mg1.t);
        String S = mg1.getT();

        Mygeneric<Integer> mg2 = new Mygeneric<Integer>();
        mg2.show(150);
        System.out.println(mg2.t);
        Integer i1 = mg2.getT();

        //Mygeneric<String> mg1=mg2;  错误

    }
}
生活
生活
150
150

泛型接口

接口

package Mygeneric;

public interface MyInterface <T>{
     public static String name= "泛型";
    T show(T t);
}

实现类

1.实现时声明类型

package Mygeneric;

public class MyInterface01 implements MyInterface<String> {
    @Override
    public String show(String s ) {
        System.out.println(s);
        System.out.println();
        return  s;
    }
}

2.调用时声明类型

package Mygeneric;

public class MyInterface02 <T> implements MyInterface<T>{
    @Override
    public T show(T t) {
        System.out.println(t);
        return t;
    }
}

测试类

package Mygeneric;

public class MyTest {
    public static void main(String[] args) {
        MyInterface01 interface01 = new MyInterface01();
        interface01.show("花好月圆");
        System.out.println(MyInterface.name);

        MyInterface02<Integer> interface02 = new MyInterface02<Integer>();
        interface02.show(1314);

    }
}
花好月圆

泛型
泛型
1314

泛型方法

public class MyGenericMethod {
    public <T> T show (T t){
        System.out.println("泛型方法"+t);
        return  t;
    }
}

  MyGenericMethod genericMethod = new MyGenericMethod();
        genericMethod.show("huhuhu");//无需声明 类型  根据输入参数决定
        genericMethod.show(200);
        genericMethod.show(3.14);
泛型方法huhuhu
泛型方法200
泛型方法3.14

转换异常正常类

需要判断数据类型能否转换

package Mygeneric;

import java.util.ArrayList;

public class Demo0 {
    public static void main(String[] args) {
        ArrayList arrayList = new ArrayList();
        arrayList.add("huahua");
        arrayList.add("gugu");
        arrayList.add(120);
        arrayList.add(520);
        for (Object obj:arrayList) {
            String s =(String) obj;
            System.out.println(s);

        }
    }

}
huahua
gugu
Exception in thread "main" java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String
	at Mygeneric.Demo0.main(Demo0.java:13)

使用泛型使集合元素为统一类型避免强类型转换异常

import java.util.ArrayList;

public class Demo0 {
    public static void main(String[] args) {
        ArrayList<String> arrayList = new ArrayList<String>();
        arrayList.add("huahua");
        arrayList.add("gugu");
        //arrayList.add(120);
        //arrayList.add(520);
        for (String str:arrayList) {
            System.out.println(str);
        }
    }
}
使用泛型约束后  int类型元素就无法添加到集合了 避免使用强类型转换

Set集合

无序无下标元素不可重复

package Set;

import java.lang.reflect.Array;
import java.util.*;

public class Demo01 {
    public static void main(String[] args) {
        //创建集合
        Set<String> set = new HashSet<>();
        //添加元素
        set.add("华为");
        set.add("小米");
        set.add("三星");
        set.add("苹果");
        set.add("魅族");
        System.out.println("元素个数为:"+set.size());
        System.out.println(set.toString());
      //遍历
        //1.增强for
        for (String str:set) {
            System.out.println(str);
        }
        //迭代器
        System.out.println("==========迭代器=========");
        Iterator it = set.iterator();
        while(it.hasNext()){
            String s =(String)it.next();
            System.out.println(s);
        }
        //判断
        System.out.println(set.contains("小米"));
        System.out.println(set.isEmpty());
        //删除
        set.remove("三星");
        System.out.println(set.toString());
        set.clear();
        System.out.println(set.toString());


    }
}
元素个数为:5
[苹果, 华为, 魅族, 小米, 三星]
苹果
华为
魅族
小米
三星
==========迭代器=========
苹果
华为
魅族
小米
三星
true
false
[苹果, 华为, 魅族, 小米]
[]

实现类

HashSet
TreeSet

HashSet

基于HashSet计算元素存放位置
当存入元素的哈希码相同时，会调用equals进行确认，若结果为true 则拒绝后者加入

存储位置哈希表（数组加链表+红黑树）

package Set.HashSet;

import java.util.HashSet;
import java.util.Iterator;

public class Demo01 {
    public static void main(String[] args) {
        //创建集合
        HashSet<String> hashSet = new HashSet<String>();
        //添加元素
        hashSet.add("刘亦菲");
        hashSet.add("杨幂");
        hashSet.add("刘诗诗");
        hashSet.add("唐嫣");
        hashSet.add("赵丽颖");
        //hashSet.add("赵丽颖");重复 不再添加
        System.out.println("元素个数为:"+hashSet.size());
        System.out.println(hashSet.toString());
        //遍历
        System.out.println("=======增强for==========");
        for (String str:hashSet) {
            System.out.println(str);
        }
        //迭代器
        System.out.println("============迭代器===========");
        Iterator it = hashSet.iterator();
        while (it.hasNext()){
            System.out.println(it.next());
        }
        //判断
        System.out.println(hashSet.contains("杨幂"));
        System.out.println(hashSet.isEmpty());
        //删除元素
        hashSet.remove("赵丽颖");
        System.out.println(hashSet.toString());
        hashSet.clear();
        System.out.println(hashSet.toString());

    }
}
元素个数为:5
[赵丽颖, 杨幂, 唐嫣, 刘亦菲, 刘诗诗]
=======增强for==========
赵丽颖
杨幂
唐嫣
刘亦菲
刘诗诗
============迭代器===========
赵丽颖
杨幂
唐嫣
刘亦菲
刘诗诗
true
false
[杨幂, 唐嫣, 刘亦菲, 刘诗诗]
[]

储存过程

(1)根据hashcode 计算保存的位置，如果此位置为空则直接保存非空则第二步

(2)执行equals方法如果equals方法为true 认为重复 false则链表

package Set.HashSet;

import java.util.Objects;

public class Person {
    private  String name;
    private  int age;

    public Person() {
    }

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Person person = (Person) o;
        return age == person.age &&
                Objects.equals(name, person.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

package Set.HashSet;

import java.util.HashSet;
import java.util.Iterator;

public class Demo02 {
    public static void main(String[] args) {
        HashSet<Person> hashSet = new HashSet<Person>();
        Person p1 = new Person("刘亦菲",33);
        Person p2 = new Person("杨幂",34);
        Person p3 = new Person("唐嫣",37);
        Person p4 = new Person("刘诗诗",33);
        Person p5 = new Person("赵丽颖",33);
        hashSet.add(p1);
        hashSet.add(p2);
        hashSet.add(p3);
        hashSet.add(p4);
        hashSet.add(p5);
        hashSet.add(new Person("赵丽颖",33));//重写后  由name age决定hashcode
        System.out.println("元素个数为:"+hashSet.size());
        System.out.println(hashSet.toString());
        //遍历
        System.out.println("==========增强for==========");
        for (Person person:hashSet) {
            System.out.println(person.toString());
        }
        System.out.println("=========迭代器=====");
        Iterator it =hashSet.iterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }
        //判断
        System.out.println(hashSet.contains(p2));
        System.out.println(hashSet.contains(new Person("赵丽颖", 33)));
        System.out.println(hashSet.isEmpty());
        //删除
        hashSet.remove(p5);
        System.out.println(hashSet.toString());
        hashSet.clear();
        System.out.println(hashSet.toString());
    }
}
元素个数为:5
[Person{name='赵丽颖', age=33}, Person{name='刘诗诗', age=33}, Person{name='刘亦菲', age=33}, Person{name='杨幂', age=34}, Person{name='唐嫣', age=37}]
==========增强for==========
Person{name='赵丽颖', age=33}
Person{name='刘诗诗', age=33}
Person{name='刘亦菲', age=33}
Person{name='杨幂', age=34}
Person{name='唐嫣', age=37}
=========迭代器=====
Person{name='赵丽颖', age=33}
Person{name='刘诗诗', age=33}
Person{name='刘亦菲', age=33}
Person{name='杨幂', age=34}
Person{name='唐嫣', age=37}
true
true
false
[Person{name='刘诗诗', age=33}, Person{name='刘亦菲', age=33}, Person{name='杨幂', age=34}, Person{name='唐嫣', age=37}]
[]

TreeSet

基于排列顺序实现元素不可重复
实现SortedSet接口对集合元素自动排序
元素对象的类型必须实现Comparable接口，指定排列顺序
通过
CompareTo方法确认是否是重复元素

package Set.TreeSet;

import Set.HashSet.Person;

import java.util.Iterator;
import java.util.TreeSet;

public class DEmo01 {
    public static void main(String[] args) {
        //创建集合
        TreeSet<Person> set = new TreeSet<>();
        //添加元素
        Person p1 = new Person("刘亦菲",33);
        Person p2 = new Person("杨幂",34);
        Person p3 = new Person("唐嫣",37);
        Person p4 = new Person("刘诗诗",33);
        Person p5 = new Person("赵丽颖",33);
        set.add(p1);//添加时 Person类必须实现Comparable接口
        set.add(p2);
        set.add(p3);
        set.add(p4);
        set.add(p5);
        System.out.println("元素个数:"+set.size());
        System.out.println(set.toString());
        //删除 remove
        set.remove(p5);
        System.out.println("元素个数:"+set.size());
        System.out.println(set.toString());
        //遍历
        System.out.println("=======增强for=====");
        for (Person person: set) {
            System.out.println(person);
        }
        System.out.println("======迭代器==========");
        Iterator it = set.descendingIterator();//倒序
        while (it.hasNext()){
            System.out.println(it.next());
        }
        //判断
        System.out.println(set.contains(p1));
        System.out.println(set.isEmpty());
    }
}
元素个数:5
[Person{name='刘亦菲', age=33}, Person{name='刘诗诗', age=33}, Person{name='唐嫣', age=37}, Person{name='杨幂', age=34}, Person{name='赵丽颖', age=33}]
元素个数:4
[Person{name='刘亦菲', age=33}, Person{name='刘诗诗', age=33}, Person{name='唐嫣', age=37}, Person{name='杨幂', age=34}]
=======增强for=====
Person{name='刘亦菲', age=33}
Person{name='刘诗诗', age=33}
Person{name='唐嫣', age=37}
Person{name='杨幂', age=34}
======迭代器==========
Person{name='杨幂', age=34}
Person{name='唐嫣', age=37}
Person{name='刘诗诗', age=33}
Person{name='刘亦菲', age=33}
true
false

还有一种定制比较器Comparator 不需要对对象类实现Comparable

package Set.TreeSet;

import Set.HashSet.Person;

import java.util.Comparator;
import java.util.TreeSet;

public class DEMO02 {
    public static void main(String[] args) {
        TreeSet<Person> set = new TreeSet<>(new Comparator<Person>() {
            @Override
            public int compare(Person o1, Person o2) {
                int n1 = o1.getName().compareTo(o2.getName());
                int n2 = o1.getAge()-o2.getAge();
                return  n1==0?n2:n1;
            }
        });
        Person p1 = new Person("刘亦菲",33);
        Person p2 = new Person("杨幂",34);
        Person p3 = new Person("唐嫣",37);
        Person p4 = new Person("刘诗诗",33);
        Person p5 = new Person("赵丽颖",33);
        set.add(p1);//添加时 Person类必须实现Comparable接口
        set.add(p2);
        set.add(p3);
        set.add(p4);
        set.add(p5);
        System.out.println("元素个数:"+set.size());
        System.out.println(set.toString());
    }
}
元素个数:5
[Person{name='刘亦菲', age=33}, Person{name='刘诗诗', age=33}, Person{name='唐嫣', age=37}, Person{name='杨幂', age=34}, Person{name='赵丽颖', age=33}]

package Set.TreeSet;

import sun.reflect.generics.tree.Tree;

import java.util.Comparator;
import java.util.Iterator;
import java.util.TreeSet;

public class Demo03 {
    public static void main(String[] args) {
        TreeSet<String> treeSet = new TreeSet<>(new Comparator<String>() {
            @Override
            public int compare(String o1, String o2) {
                int n1= o1.length()-o2.length();
                int n2 = o1.compareTo(o2);
                return n1==0?n2:n1;
            }
        });
        //添加元素
        treeSet.add("qingdao");
        treeSet.add("zaozhuang");
        treeSet.add("tengzhou");
        treeSet.add("nanjing");
        treeSet.add("jinan");
        System.out.println("城市个数为:"+treeSet.size());
        System.out.println(treeSet.toString());
        //遍历
        //增强for
        System.out.println("=======增强for=========");
        for (String str:treeSet) {
            System.out.println(str);
        }
        //迭代
        System.out.println("==========迭代器=====");
        Iterator iterator = treeSet.descendingIterator();
        while (iterator.hasNext()){
            System.out.println(iterator.next());
        }
        //判断
        System.out.println(treeSet.contains("jinan"));
        System.out.println(treeSet.isEmpty());
        //删除
        System.out.println(treeSet.remove("jinan"));
        treeSet.clear();

    }
}
城市个数为:5
[jinan, nanjing, qingdao, tengzhou, zaozhuang]
=======增强for=========
jinan
nanjing
qingdao
tengzhou
zaozhuang
==========迭代器=====
zaozhuang
tengzhou
qingdao
nanjing
jinan
true
false
true

Map

java集合--千锋教育

Map:

存储键值对
键不能重复，值可以重复
无序

package Map;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class Demo0 {
    public static void main(String[] args) {
        //添加元素
        Map<String,String> map =new HashMap<>();
        map.put("没头脑","不高兴");
        map.put("汤姆","杰瑞");
        map.put("喜羊羊","美羊羊");
        map.put("喜羊羊","灰太狼");
        map.put("虹猫","蓝兔");
        System.out.println("键值对个数:"+map.size());
        System.out.println(map.toString());
        Map<String,String> map2 =new HashMap<>();
        map2.putAll(map);//复制全部
        System.out.println("键值对个数:"+map2.size());
        System.out.println(map2.toString());
        //判断
        System.out.println(map.containsKey("没头脑"));//判断是否包含键
        System.out.println(map.containsValue("蓝兔"));//判断是否包含值
        System.out.println(map.isEmpty());
        //迭代
        System.out.println( "=============keyset迭代========");
        for (String key:map.keySet()) {
            System.out.println(key+"-->"+map.get(key));
        }
        //entryset迭代
        System.out.println("============entryset迭代=============");
        //Set<Map.Entry<String,String>> entry=map.entrySet();
        for(Map.Entry<String,String> entry:map.entrySet()){
            System.out.println(entry);
        }

        //视图
        System.out.println(map.entrySet());//返回映射对
        System.out.println(map.keySet());//返回键
        System.out.println(map.values());//返回值
        //其他
        System.out.println(map.get("汤姆"));//返回键对应值


    }
}
键值对个数:4
{虹猫=蓝兔, 没头脑=不高兴, 喜羊羊=灰太狼, 汤姆=杰瑞}
键值对个数:4
{虹猫=蓝兔, 没头脑=不高兴, 喜羊羊=灰太狼, 汤姆=杰瑞}
true
true
false
=============keyset迭代========
虹猫-->蓝兔
没头脑-->不高兴
喜羊羊-->灰太狼
汤姆-->杰瑞
============entryset迭代=============
虹猫=蓝兔
没头脑=不高兴
喜羊羊=灰太狼
汤姆=杰瑞
[虹猫=蓝兔, 没头脑=不高兴, 喜羊羊=灰太狼, 汤姆=杰瑞]
[虹猫, 没头脑, 喜羊羊, 汤姆]
[蓝兔, 不高兴, 灰太狼, 杰瑞]
杰瑞

实现类

HashMap

默认容量16 0.75 扩容

package Map.HashMap;

import java.util.Objects;

public class Student {
    private String name;
    private int StuTo;

    public Student(String name, int stuTo) {
        this.name = name;
        StuTo = stuTo;
    }

    public Student() {
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getStuTo() {
        return StuTo;
    }

    public void setStuTo(int stuTo) {
        StuTo = stuTo;
    }

    @Override
    public String toString() {
        return "Student{" + "name='" + name + '\'' + ", StuTo=" + StuTo + '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Student)) return false;
        Student student = (Student) o;
        return StuTo == student.StuTo &&
                Objects.equals(name, student.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, StuTo);
    }
}

package Map.HashMap;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class Demo00 {
    public static void main(String[] args) {
        //创建集合
        HashMap<Student, String> students = new HashMap<Student, String>();
        //添加元素
        Student s1 = new Student("周杰伦",20200001);
        Student s2 = new Student("林俊杰",20200002);
        Student s3 = new Student("王力宏",20200003);
        Student s4 = new Student("张杰",20200004);
        Student s5 = new Student("薛之谦",20200005);
        students.put(s1,"屋顶");
        students.put(s2,"一眼万年");
        students.put(s3,"真的爱你");
        students.put(s4,"天下");
        students.put(s5,"其实");
        students.put(new Student("薛之谦",20200005),"其实");//重写hashcode和equals后 由name StuTo判断相等
        System.out.println("歌手与其作品:"+students.size());
        System.out.println(students.toString());//无序排列
        //迭代
        System.out.println("==========keySet=======");
        for (Student student:students.keySet()) {
            System.out.println(student+"-->"+students.get(student));
        }
        System.out.println("=========EntrySet=============");
        for (Map.Entry<Student,String> entry: students.entrySet()){
            System.out.println(entry);
        }
        //判断
        System.out.println(students.containsKey(s1));
        System.out.println(students.containsValue("认真的雪"));
        //删除
        System.out.println(students.remove(s1));//删除键 返回值
        System.out.println(students.toString());//无序排列
        System.out.println(students.remove(s2,"江南"));
        System.out.println(students.remove(s2,"一眼万年"));
        students.clear();
        System.out.println(students.toString());//无序排列

    }
}
歌手与其作品:5
{Student{name='张杰', StuTo=20200004}=天下, Student{name='周杰伦', StuTo=20200001}=屋顶, Student{name='林俊杰', StuTo=20200002}=一眼万年, Student{name='薛之谦', StuTo=20200005}=其实, Student{name='王力宏', StuTo=20200003}=真的爱你}
==========keySet=======
Student{name='张杰', StuTo=20200004}-->天下
Student{name='周杰伦', StuTo=20200001}-->屋顶
Student{name='林俊杰', StuTo=20200002}-->一眼万年
Student{name='薛之谦', StuTo=20200005}-->其实
Student{name='王力宏', StuTo=20200003}-->真的爱你
=========EntrySet=============
Student{name='张杰', StuTo=20200004}=天下
Student{name='周杰伦', StuTo=20200001}=屋顶
Student{name='林俊杰', StuTo=20200002}=一眼万年
Student{name='薛之谦', StuTo=20200005}=其实
Student{name='王力宏', StuTo=20200003}=真的爱你
true
false
屋顶
{Student{name='张杰', StuTo=20200004}=天下, Student{name='林俊杰', StuTo=20200002}=一眼万年, Student{name='薛之谦', StuTo=20200005}=其实, Student{name='王力宏', StuTo=20200003}=真的爱你}
false
true
{}

java集合--千锋教育

刚创建hashmap table=null size=0 传入一个元素后 size=1<<4(16)

当传输到16*0.75=12时扩容到原来2倍64 以此类推

java集合--千锋教育

Hashtable

properties

TreeMap

package Map.TreeMap;

import Map.HashMap.Student;

import java.util.Comparator;
import java.util.Map;
import java.util.TreeMap;

public class Demo00 {
    public static void main(String[] args) {
        //创建集合 用定制比较器 或使类实现 Comparable
        TreeMap<Student, String> students = new TreeMap<>(new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                int n1 =  o1.getName().compareTo(o2.getName());
                int n2 = o1.getStuTo()-o2.getStuTo();
                return n1==0?n2:n1;
            }
        });
        Student s1 = new Student("周杰伦",20200001);
        Student s2 = new Student("林俊杰",20200002);
        Student s3 = new Student("王力宏",20200003);
        Student s4 = new Student("张杰",20200004);
        Student s5 = new Student("薛之谦",20200005);
        students.put(s1,"屋顶");
        students.put(s2,"一眼万年");
        students.put(s3,"真的爱你");
        students.put(s4,"天下");
        students.put(s5,"其实");
        students.put(new Student("薛之谦",20200005),"其实");//重写hashcode和equals后 由name StuTo判断相等
        System.out.println("歌手与其作品:"+students.size());
        System.out.println(students.toString());//无序排列
        //迭代
        System.out.println("=======keySet()=========");
        for (Student key:students.keySet()) {
            System.out.println(key+"----------"+students.get(key));
        }
        System.out.println("============entrySet()===========");
        for(Map.Entry<Student,String> entry: students.entrySet()){
            System.out.println(entry.getKey()+"------"+entry.getValue());
        }
        ///判断
        System.out.println(students.containsKey(s1));
        System.out.println(students.containsValue("认真的雪"));
        System.out.println(students.isEmpty());
        //移除
        students.remove(s1);
        System.out.println("歌手与其作品:"+students.size());
        students.clear();
        System.out.println("歌手与其作品:"+students.size());

    }
}
歌手与其作品:5
{Student{name='周杰伦', StuTo=20200001}=屋顶, Student{name='张杰', StuTo=20200004}=天下, Student{name='林俊杰', StuTo=20200002}=一眼万年, Student{name='王力宏', StuTo=20200003}=真的爱你, Student{name='薛之谦', StuTo=20200005}=其实}
=======keySet()=========
Student{name='周杰伦', StuTo=20200001}----------屋顶
Student{name='张杰', StuTo=20200004}----------天下
Student{name='林俊杰', StuTo=20200002}----------一眼万年
Student{name='王力宏', StuTo=20200003}----------真的爱你
Student{name='薛之谦', StuTo=20200005}----------其实
============entrySet()===========
Student{name='周杰伦', StuTo=20200001}------屋顶
Student{name='张杰', StuTo=20200004}------天下
Student{name='林俊杰', StuTo=20200002}------一眼万年
Student{name='王力宏', StuTo=20200003}------真的爱你
Student{name='薛之谦', StuTo=20200005}------其实
true
false
false
歌手与其作品:4
歌手与其作品:0

Collections

package Collections;

import java.lang.reflect.Array;
import java.util.*;

public class Demo01 {
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<>();
        //添加元素
        list.add(20);
        list.add(6);
        list.add(12);
        list.add(25);
        list.add(30);
        System.out.println("元素个数:" + list.size());
        System.out.println(list.toString());
        //排列
        Collections.sort(list);
        System.out.println(list.toString());
        //二叉树查找 排序之后
        int s = Collections.binarySearch(list, 20);//存在返回索引值 不存在为负
        System.out.println(s);
        //倒序
        Collections.reverse(list);
        System.out.println(list);
        //乱序
        Collections.shuffle(list);
        System.out.println(list);
        //copy复制
        List<Integer> list1 = new ArrayList();
        for (int i = 0; i < list.size(); i++) {
            list1.add(0);
        }
        Collections.copy(list1,list);//IndexOutOfBoundsException  要求复制的列表大小一致
        System.out.println(list1);

        //其他
        //list转为数组
        System.out.println("===list转为数组===");
        Integer[] array = list.toArray(new Integer[0]);//参数小于list元素个数时 得到的数组大小为list.size  大于则为参数大小 其余以null填充
        System.out.println(Arrays.toString(array));
        System.out.println(array.length);
        //数组转为列表
        System.out.println("====数组转为列表========");
        String[] singer= {"邓紫棋","毛不易","廖俊涛"};
        //数组转为的列表为受限列表 不能添加或删除
        List list2= Arrays.asList(singer);
        System.out.println(list2);
        //基本类型转换时 需要用包装类型
        //int[] i1= {10,20,100,200};
        //List<int>  list3 =Arrays.asList(i1);  报错
        Integer[] i1= {10,20,100,200};
        List<Integer>  list3 =Arrays.asList(i1);
        System.out.println(list3);

    }
}
元素个数:5
[20, 6, 12, 25, 30]
[6, 12, 20, 25, 30]
2
[30, 25, 20, 12, 6]
[20, 25, 6, 30, 12]
[20, 25, 6, 30, 12]
===list转为数组===
[20, 25, 6, 30, 12]
5
====数组转为列表========
[邓紫棋, 毛不易, 廖俊涛]
[10, 20, 100, 200

数组特点：大小固定，只能存储相同数据类型的数据

集合特点：大小可动态扩展，可以存储各种类型的数据

上一篇： Stack | 栈的数组实现

下一篇：商品绑定可用的优惠券(多对多的绑定且一张优惠券只能使用于一个商品)

java集合--千锋教育

集合

一、集合概念

Collection体系

父接口

List

List 实现类

泛型参数化类型

泛型类

泛型接口

泛型方法

转换异常正常类

Set集合

实现类

HashSet

TreeSet

Map

实现类

HashMap

Hashtable

TreeMap

Collections