Map接口-白红宇

Map接口

阅读量：5259 次

发布时间：2019-06-14

本文共 4221 字，大约阅读时间需要 14 分钟。

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
     
       map=new HashMap
      
       ();        //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
       
         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
        
          key1=map.keySet();        Iterator
         
           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
          
           
            > entrys=map.entrySet(); for(Map.Entry
            
              entry:entrys){ String key=entry.getKey(); String value=entry.getValue(); System.out.println(key+value); } //Interator迭代器迭代 Set
             
              
               > entry1=map.entrySet(); Iterator
               
                
                 > it1=entry1.iterator(); while(it1.hasNext()){ //获取每一张结婚证 Map.Entry
                 
                   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
                  
                    map=new HashMap
                   
                    (); 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
                    
                      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
     
       map=new HashMap
      
       ();        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
       
         set=map.keySet();        for(Person s:set){                                System.out.println(s+map.get(s));        }                                         }

//有序遍历     public static void method3(){        Map
     
       map=new LinkedHashMap
      
       ();        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
       
         set=map.keySet();        for(Person s:set){                                 System.out.println(s+map.get(s));        }                                         }                                        }