Map中的方法实例代码（遗忘再回来看一下）

最新推荐文章于 2023-06-19 18:37:29 发布

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本文通过具体示例展示了如何使用 Java 中的 HashMap 进行增删改查操作，包括添加元素、检查键与值的存在状态、遍历集合等。此外，还讨论了如何重写 equals 方法以实现更精确的对象匹配。

package com.xiaodong;

import java.util.HashMap;

import java.util.Map;

import java.util.Set;

import java.util.Map.Entry;

public class Text1

{

public static void main(String[] args)

{

run(); //打印Map集合

run1(); //将对象作为值打印集合,以及重写equals方法判断是否包含对象的值

run2(); //不重写equals方法判断是否包含这个对象的值的方法

run3(); //判断这个集合是否为空

run4(); //遍历map集合

}

public static void run()

{

//创建一个以字符串作为键,Peek对象作为值的集合

Map<String,Peek> map = new HashMap<String,Peek>();

map.put("key1", new Peek(1,"张三",21));

map.put("key2", new Peek(2,"李四",23));

map.put("key3", new Peek(3,"王五",22));

map.put("key4", new Peek(4,"刘六",25));

System.out.println(map);

}

public static void run1()

{

//创建一个以字符串作为键,Peek对象作为值的集合

Map<String,Peek> map = new HashMap<String,Peek>();

map.put("key1", new Peek(1,"张三",21));

map.put("key2", new Peek(2,"李四",23));

map.put("key3", new Peek(3,"王五",22));

map.put("key4", new Peek(4,"刘六",25));

//是否包含指定的键

boolean is = map.containsKey("key1");

System.out.println(is);

//是否包含指定的值

boolean is1 = map.containsValue(new Peek(2,"李四",23));

System.out.println(is1);

}

public static void run2()

{

//不重写equals方法的判断方法

Peek p = new Peek(1,"张三",21);

Map<String,Peek> map = new HashMap<String,Peek>();

map.put("key1", new Peek(1,"张三",21));

map.put("key2", new Peek(2,"李四",23));

map.put("key3", new Peek(3,"王五",22));

map.put("key4", new Peek(4,"刘六",25));

boolean is = map.containsValue(p);

System.out.println(is);

}

public static void run3()

{

Map<String,Peek> map = new HashMap<String,Peek>();

map.put("key1", new Peek(1,"张三",21));

map.put("key2", new Peek(2,"李四",23));

map.put("key3", new Peek(3,"王五",22));

map.put("key4", new Peek(4,"刘六",25));

map.clear();

//判断这个集合是否为空

boolean is = map.isEmpty();

System.out.println(is);

}

public static void run4()

{

Map<String,Peek> map = new HashMap<String,Peek>();

map.put("key1", new Peek(1,"张三",21));

map.put("key2", new Peek(2,"李四",23));

map.put("key3", new Peek(3,"王五",22));

map.put("key4", new Peek(4,"刘六",25));

Set<Entry<String,Peek>> ti = map.entrySet();

for(Entry<String,Peek> s : ti)

{

//获得键

String t = s.getKey();

System.out.print("键:"+t);

//获得值

Peek t1 = s.getValue();

System.out.println("值:"+t1);

}

class Peek

{

private int id;

private String name;

private int age;

public int getId() {

return id;

}

public void setId(int id) {

this.id = id;

}

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;

}

public Peek(int id, String name, int age) {

super();

this.id = id;

this.name = name;

this.age = age;

}

@Override

public String toString() {

return "Peek [age=" + age + ", id=" + id + ", name=" + name + "]";

}

//判断包含指定的值需要重写equals方法

public boolean equals(Object obj)

{

if(!(obj instanceof Peek))

{

return false;

}

Peek pe = (Peek)obj;

if(this.id == pe.id&&this.age == pe.age&&this.name == pe.name)

{

return true;

}

return false;

}

//重写hashCode方法

public int hashCode()

{

return 1;

}