Map接口

Map接口中的常用方法
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
//Map接口
public class Demo01 {
    public static void main(String[] args) {
        Map<String,String> map=new HashMap<String,String>();
        //添加元素
        map.put("a", "1");
        map.put("b", "2");
        map.put("a", "3");//key键不能重复   如果重复会覆盖值            值可以重复
        map.put("c", "1");
        /*String v=map.remove("b");
        //查询元素
        System.out.println(map.get("a"));
        System.out.println(map.get("b"));
        System.out.println(map.get("c"));*/
Map集合遍历键找值方式
        //1.通过keyset遍历map
        //增强for
        Set<String> keys=map.keySet();
        for(String key:keys){
            System.out.print(key);//取key
            System.out.println(map.get(key));//取值
        }
        //Interator迭代器迭代
        Set<String> key1=map.keySet();
        Iterator<String> it=key1.iterator();
        while(it.hasNext()){
            String key=it.next();
            String value=map.get(key);
            System.out.println(key+value);
        }
Map集合遍历键值对方式
        //2.entrySet方法遍历
        //增强for
        Set<Map.Entry<String, String>> entrys=map.entrySet();
        for(Map.Entry<String, String> entry:entrys){
            String key=entry.getKey();
            String value=entry.getValue();
            System.out.println(key+value);
        }
        //Interator迭代器迭代
        Set<Map.Entry<String, String>> entry1=map.entrySet();
        Iterator<Map.Entry<String, String>> it1=entry1.iterator();
        while(it1.hasNext()){
            //获取每一张结婚证
            Map.Entry<String, String> entry=it1.next();
            String key=entry.getKey();//从结婚证上获取key
            String value=entry.getValue();//从结婚证上获取值
            System.out.println(key+value);
        }
    }
}
HashMap存储自定义类型键值
先建一个Person类
public class Person {
    private String name;
    private int 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;
    }
    public Person(){}
    public Person(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    public String toString() {
        return "Person [name=" + name + ", age=" + age + "]";
    }
    
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + age;
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        return result;
    }
    
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Person other = (Person) obj;
        if (age != other.age)
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        return true;
    }
    
}

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

public class Demo02 {
    public static void main(String[] args) {
        method1();
        method2();
        method3();
    }
    public static void method1(){
        Map<String,Person> map=new HashMap<String,Person>();
        map.put("2", new Person("帅涛",18));
        map.put("1", new Person("狗炜",19));
        map.put("3", new Person("小菜",19));
        map.put("4", new Person("小明",19));
        map.put("4", new Person("小明",19));
        //遍历
        Set<String> set=map.keySet();
        for(String s:set){                     
            System.out.println(s+map.get(s));
        }                                     
    }

 

//自定义类型当key键时需要重写hashCode和equals方法
    public static void method2(){
        Map<Person,String> map=new HashMap<Person,String>();
        map.put(new Person("帅涛",18),"1" );
        map.put(new Person("狗炜",19),"2" );
        map.put(new Person("小菜",19),"3");
        map.put(new Person("小明",19),"4" );
        map.put(new Person("小明",19),"4" );
        //遍历
        Set<Person> set=map.keySet();
        for(Person s:set){                    
            System.out.println(s+map.get(s));
        }                                     
    }

//有序遍历 
    public static void method3(){
        Map<Person,String> map=new LinkedHashMap<Person,String>();
        map.put(new Person("帅涛",18),"2" );
        map.put(new Person("狗炜",19),"1" );
        map.put(new Person("小菜",19),"3");
        map.put(new Person("小明",19),"4" );
        map.put(new Person("小明",19),"4" );
        //遍历
        Set<Person> set=map.keySet();
        for(Person s:set){                     
            System.out.println(s+map.get(s));
        }                                     
    }                                        
}