Java 集合框架(链表、集合、映射)，适合Java初学者

本文参考自我的Java老师，详情看代码注释，有写得不明白的地方欢迎留言，有错误地方欢迎大佬批评指正

目录结构

Cat类是共用的，在不同的框架会相对应的更改

一、链表

List链表是一种有序集合，也称为序列。
常用的有ArrayList和LinedList

1.0 Cat

package connection.List;

public class Cat{
    private String name;
    private int age;
    //无参构造
    public Cat(){}
    //全参构造
    public Cat(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;
    }
}

1.1 ArrayList

package connection.List;

import java.util.Iterator;
import java.util.List;

public class ArrayList {
    public static void main(String[] args) {
        Cat tomcat=new Cat();
        tomcat.setName("Tom");

        Cat JackCat = new Cat();
        JackCat.setName("Jack");

        Cat JohnCat=new Cat();
        JohnCat.setName("John");

        Cat AnnCat=new Cat();
        AnnCat.setName("Ann");

        List<Cat> cats=new java.util.ArrayList<Cat>();
        cats.add(tomcat);
        cats.add(JackCat);
        cats.add(JohnCat);

        System.out.print("First value of list:");
        System.out.println(cats.get(0).getName());


        cats.set(0,JackCat);
        System.out.print("First value of list:");
        System.out.println(cats.get(0).getName());

        //判断元素及其位置
        System.out.print("Dose list 'cats' contains 'JackCat'? ");
        System.out.println(cats.contains(JackCat));
        System.out.print("So,tell me the index of JackCat in list 'cats':");
        System.out.println(cats.indexOf(JackCat));

        //清除元素
        //cats.clear();

        //链表判空
        System.out.print("Is the list empty?:");
        System.out.println(cats.isEmpty());

        //ArrayList转化为数组1
        System.out.print("Turn ArrayList to Array: ");
        Cat[] c=cats.toArray(new Cat[0]);
        System.out.println(c[0].getName());

        //ArrayList转化为数组1
        Cat[] array=new Cat[cats.size()];
        cats.toArray(array);
        for (int i = 0; i < array.length; i++) {
            System.out.print(array[i].getName()+" ");
        }
        System.out.println();
        //遍历
        //1、通过索引访问
        System.out.println("traversal thought index:");
        for (int i = 0; i < cats.size(); i++) {
            System.out.print(cats.get(i).getName()+" ");
        }
        System.out.println();
        //2、通过迭代器访问
        System.out.println("traversal thought iterator:");
        Iterator it=cats.iterator();
        while (it.hasNext()){
            Cat cat=(Cat) it.next();
            System.out.print(cat.getName()+" ");
        }
        System.out.println();
        //3、通过ForEach循环遍历
        System.out.println("traversal thought ForEach");
        for (Cat cat:cats){
            System.out.print(cat.getName()+" ");
        }
    }
}

1.2 LinkedList

package connection.List;

public class LinkedList {
    public static void main(String[] args) {
        Cat tomcat=new Cat();
        tomcat.setName("Tom");

        Cat JackCat = new Cat();
        JackCat.setName("Jack");

        Cat JohnCat=new Cat();
        JohnCat.setName("John");

        Cat AnnCat=new Cat();
        AnnCat.setName("Ann");
        // 新建一个LinkedList
        java.util.LinkedList<Cat> stack=new java.util.LinkedList<Cat>();
        // 元素压入栈中
        stack.push(tomcat);
        stack.push(JackCat);
        stack.push(JohnCat);
        stack.push(AnnCat);

        // 删除栈顶元素
        System.out.println("stack.pop():"+stack.pop().getName());

        // 取出栈顶元素
        System.out.println("stack.peek():"+stack.peek().getName());
    }
}

二、集合

2.0 Cat 类

package connection.List;

public class Cat implements Comparable{
    private String name;
    private int age;
    public Cat(){}
    public Cat(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
    //通过年龄进行比较
    public int compareTo(Object o) {
        if(!(o instanceof Cat)){
            throw new RuntimeException("Not the Object of 'Cat'");
        }
        //强制类型转换
        Cat p =(Cat)o;
        if(this.age>p.age){
            return 1;
        }
        //年龄相同则根据名字的字典序排序
        if(this.age==p.age) {
            return this.name.compareTo(p.name);
        }
        return -1;
    }
}

2.1 HashSet

package connection.set;

import connection.List.Cat;

import java.util.*;


/**
 * HashSet是无序得，由HashMap实现
 */
public class HashSetTest {
    public static void main(String[] args) {
        Cat tomcat=new Cat();
        tomcat.setName("Tom");

        Cat JackCat = new Cat();
        JackCat.setName("Jack");

        Cat JohnCat=new Cat();
        JohnCat.setName("John");

        Cat AnnCat=new Cat();
        AnnCat.setName("Ann");

        Set<Cat> cats=new HashSet<>();
        //tomcat加了两次
        cats.add(tomcat);
        cats.add(tomcat);

        cats.add(JackCat);
        cats.add(JohnCat);

        // 通过迭代器访问可以看到，Set不允许有重复元素
        Iterator<Cat> it=cats.iterator();
        while (it.hasNext()){
            Cat cat=it.next();
            System.out.println(cat.getName());
        }
    }
}

2.2 TreeSet

package connection.set;

import connection.List.Cat;

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

/**
 * TreeSet 是一个有序的集合，它的作用是提供有序的Set集合.
 * TreeSet中的元素支持2种排序方式.
 * 自然排序或者根据创建TreeSet时提供的 Comparator 进行排序.
 */
public class TreeSetTest {
    public static void main(String[] args) {
        Set<Cat> cats=new TreeSet<>();

        Cat tomcat = new Cat();
        tomcat.setName("Tom");
        tomcat.setAge(8);

        Cat JackCat = new Cat();
        JackCat.setName("Jack");
        JackCat.setAge(4);

        Cat JohnCat = new Cat();
        JohnCat.setName("John");
        JohnCat.setAge(6);

        Cat AnnCat = new Cat();
        AnnCat.setName("Ann");
        //插入数据
        cats.add(tomcat);
        cats.add(tomcat);
        cats.add(JackCat);
        cats.add(JohnCat);

        Iterator<Cat> it=cats.iterator();
        while (it.hasNext()){
            Cat cat=it.next();
            System.out.println(cat.getName());
        }
    }

}

三、映射

3.0 Cat类与上相同

3.1 HashMap

package connection.map;
/**
 * Map是映射接口，Map中存储的内容是键值对(key-value).
 * Map映射中不能包含重复的键，每个键最多只能映射到一个值
 */

import connection.List.Cat;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

/**
 *HashMap 继承于AbstractMap，但没实现NavigableMap接口.
 * 因此，HashMap的内容是“键值对，但不保证次序”.
 */
public class HashMapTest {
    public static void main(String[] args) {
        Map<String, Cat> cats=new HashMap<String,Cat>();
        cats.put("Tom",new Cat("Tom",2));
        cats.put("Jack",new Cat("Jack",5));
        cats.put("John",new Cat("John",7));

        Cat cat=cats.get("Tom");
        System.out.println(cat.getName());

        Iterator iter=cats.entrySet().iterator();

        while (iter.hasNext()){
            Map.Entry entry=(Map.Entry) iter.next();
            System.out.println("next:"+entry.getKey()+"-"+((Cat)entry.getValue()).getName()+((Cat)entry.getValue()).getAge());
        }

    }
}

3.2 TreeMap

package connection.map;

/**
 * Map是映射接口，Map中存储的内容是键值对(key-value).
 * Map映射中不能包含重复的键，每个键最多只能映射到一个值
 */


import connection.List.Cat;

import java.util.Iterator;
import java.util.Map;
import java.util.TreeMap;

/**
 * Tree继承于AbstractMap，实现Map接口.
 * TreeMap 是一个有序的 key-value，它是通过红黑树实现的
 */
public class TreeMapTest {
    public static void main(String[] args) {
        Map<String, Cat> cats=new TreeMap<String, Cat>();
        cats.put("Tom",new Cat("Tom",2));
        cats.put("Jack",new Cat("Jack",2));
        cats.put("John",new Cat("hello",12));

        Cat cat=cats.get("John");
        System.out.println(cat.getName()+" "+cat.getAge());

        Iterator iter=cats.entrySet().iterator();
        while (iter.hasNext()){
            Map.Entry entry=(Map.Entry) iter.next();
            System.out.println("next:"+entry.getKey()+
                    "-"+((Cat)entry.getValue()).getName()+
                    "-"+((Cat)entry.getValue()).getAge());
        }

    }
}

本文地址：https://blog.csdn.net/weixin_45728842/article/details/110879799