java Map练习

程序员文章站 2022-12-08 21:30:13

描述学生，map容器，学生为键，地址为值，获取map中的元素。 public class MapDemo { public static void main(String[] args) { HashMap hm = new HashMap

描述学生，map容器，学生为键，地址为值，获取map中的元素。

public class mapdemo {
    public static void main(string[] args) {
        hashmap<student, string> hm = new hashmap<student, string>();
        hm.put(new student("lisi1", 1), "北京");
        hm.put(new student("lisi2", 2), "上海");
        hm.put(new student("lisi3", 3), "天津");
        hm.put(new student("lisi4", 4), "武汉");
        //第一种取出方式 keyset
        set<student> keyset = hm.keyset();
        iterator<student> it = keyset.iterator();
        while (it.hasnext()) {
            student stu = it.next();
            string addr = hm.get(stu);
            system.out.println(stu + "--" + addr);
        }
        //第二种取出方式 entryset
        set<map.entry<student, string>> entryset = hm.entryset();
        iterator<map.entry<student, string>> i = entryset.iterator();
        while (i.hasnext()) {
            map.entry<student, string> stu = i.next();
            system.out.println(stu.getkey() + "--" + stu.getvalue());
        }

    }
}

class student implements comparable<student> {
    private string name;
    private int age;

    public student(string name, int age) {
        this.name = name;
        this.age = age;
    }

    @override
    public boolean equals(object obj) {
        if (!(obj instanceof student))
            throw new classcastexception("类型不匹配");
        student s = (student) obj;
        return this.name.equals(s.name) && this.age == s.age;
    }

    @override
    public int hashcode() {
        return name.hashcode() + age * 34;
    }

    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 string tostring() {
        return "student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    @override
    public int compareto(student o) {
        int num = new integer(this.age).compareto(new integer(o.age));
        if (num == 0) {
            return this.name.compareto(o.name);
        }
        return num;
    }
}

排序年龄：

public class mapdemo {
    public static void main(string[] args) {
        treemap<student, string> tm = new treemap<student, string>();
        tm.put(new student("lisi4", 1), "武汉");
        tm.put(new student("lisi1", 4), "北京");
        tm.put(new student("lisi3", 2), "天津");
        tm.put(new student("lisi2", 3), "上海");

        set<map.entry<student, string>> entryset = tm.entryset();
        iterator<map.entry<student, string>> it = entryset.iterator();
        while (it.hasnext()) {
            map.entry<student, string> stu = it.next();
            system.out.println(stu.getkey() + "--" + stu.getvalue());
        }

    }
}

class student implements comparable<student> {
    private string name;
    private int age;

    public student(string name, int age) {
        this.name = name;
        this.age = age;
    }

    @override
    public boolean equals(object obj) {
        if (!(obj instanceof student))
            throw new classcastexception("类型不匹配");
        student s = (student) obj;
        return this.name.equals(s.name) && this.age == s.age;
    }

    @override
    public int hashcode() {
        return name.hashcode() + age * 34;
    }

    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 string tostring() {
        return "student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    @override
    public int compareto(student o) {
        int num = new integer(this.age).compareto(new integer(o.age));
        if (num == 0) {
            return this.name.compareto(o.name);
        }
        return num;
    }
}

姓名排序：

public class mapdemo {
    public static void main(string[] args) {
        treemap<student, string> tm = new treemap<student, string>(new stucomparator());
        tm.put(new student("lisi4", 1), "武汉");
        tm.put(new student("lisi1", 4), "北京");
        tm.put(new student("lisi3", 2), "天津");
        tm.put(new student("lisi2", 3), "上海");

        set<map.entry<student, string>> entryset = tm.entryset();
        iterator<map.entry<student, string>> it = entryset.iterator();
        while (it.hasnext()) {
            map.entry<student, string> stu = it.next();
            system.out.println(stu.getkey() + "--" + stu.getvalue());
        }

    }
}

class student implements comparable<student> {
    private string name;
    private int age;

    public student(string name, int age) {
        this.name = name;
        this.age = age;
    }

    @override
    public boolean equals(object obj) {
        if (!(obj instanceof student))
            throw new classcastexception("类型不匹配");
        student s = (student) obj;
        return this.name.equals(s.name) && this.age == s.age;
    }

    @override
    public int hashcode() {
        return name.hashcode() + age * 34;
    }

    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 string tostring() {
        return "student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    @override
    public int compareto(student o) {
        int num = new integer(this.age).compareto(new integer(o.age));
        if (num == 0) {
            return this.name.compareto(o.name);
        }
        return num;
    }
}

class stucomparator implements comparator<student> {

    @override
    public int compare(student o1, student o2) {
        int num = o1.getname().compareto(o2.getname());
        if (num == 0)
            return new integer(o1.getage()).compareto(new integer(o2.getage()));
        return num;
    }
}

获取字符串("aabbbcccccdfff")中字母出现的次数：

希望打印结果：a(1)c(2)......

有映射关系先想到map集合。

1.将字符串转换成字符数组，因为要对每一个字母进行操作

2.定义map集合，打印结果有顺序，使用treemap

3.遍历字符数组，将每一个字母作为键去查map集合，返回null，就将该字母和1存入map集合中，返回不是null，获取次数加1，在存入集合，覆盖原来的键值对。

4.将map集合的数据变成指定的字符串形式返回。

public class demo {
    public static void main(string[] args) {
        string s = charcount("aa+++___bbbcccccdfff");
        system.out.println(s);
    }

    public static string charcount(string str) {
        char[] chs = str.tochararray();
        treemap<character, integer> tm = new treemap<character, integer>();
        int count = 0;
        for (int i = 0; i < chs.length; i++) {
            if (!(chs[i]>='a' && chs[i]<='z' || chs[i]>='a' && chs[i]<='z'))
                continue;
            integer value = tm.get(chs[i]);
            if (value != null)
                count = value;
            count++;
            tm.put(chs[i], count);
            count = 0;
        }
        stringbuilder sb = new stringbuilder();
        set<map.entry<character, integer>> entryset = tm.entryset();
        iterator<map.entry<character, integer>> it = entryset.iterator();
        while (it.hasnext()) {
            map.entry<character, integer> me = it.next();
            character ch = me.getkey();
            integer value = me.getvalue();
            sb.append(ch + "(" + value + ")");
        }
        return sb.tostring();
    }
}

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