# Map 基本操作和常用方法

Map 基本操作和常用方法

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找出Map中Values的最大和最小值（Arrays.sort(object)）

@Test
public void test1(){
    Map<String, String> map=new HashMap<>();
    map.put("4","5");
    map.put("5","8");
    map.put("6","9");
    map.put("7","7");
    Collection<String> values = map.values();
    Object[] objects = values.toArray();
    Arrays.sort(objects);
    String min = String.valueOf(objects[0]);
    String max = objects[objects.length - 1].toString();
    System.out.println("最大和最小值为："+max+"===="+min);
}

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map.get() 或者map.getOrDefault()

• map.get(“test”)：当值为空时候返回null
• map.getOrDefault(“test”)：当值为空时候可以给给定默认值

@Test
public void test6() {
    Map<String, String> map = new HashMap<>();
    map.put("6", "9");
    map.put("7", "7");
    String test = map.get("test");
    String test1 = map.getOrDefault("test", "test1");
    System.out.println(test);
    System.out.println(test1);
}

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判断集合为空 map.isEmpty()

@Test
public void test6() {
    Map<String, String> map = new HashMap<>();
    Map<String, String> map1=new HashMap<>();
    boolean empty = map.isEmpty(); # false
    boolean empty1 = map1.isEmpty(); #true
}

---

Map遍历

map.foreach()

@Test
public void test2(){
    Map<String, String> map=new HashMap<>();
    map.put("6","9");
    map.put("7","7");
    map.forEach((x,y)->{
        System.out.println("键值为："+x+"===="+y);
    });
}

Map的Entry

@Test
public void test3(){
    Map<String, String> map=new HashMap<>();
    map.put("6","9");
    map.put("7","7");
    for(Map.Entry entry:map.entrySet()){
        System.out.println(entry.getKey()+"====="+entry.getValue());
    }
}

For循环map.keyset()

@Test
public void test4(){
    Map<String, String> map=new HashMap<>();
    map.put("6","9");
    map.put("7","7");
    for(String entry:map.keySet()){
        System.out.println(entry+"===="+map.get(entry));
    }
}

---

得到Map中的所有Values map.values()

@Test
public void test5(){
    Map<String, String> map=new HashMap<>();
    map.put("6","9");
    map.put("7","7");
    Collection<String> values = map.values();
    System.out.println(values);
}

。。。未完待续