java Map集合中取键和值的4种方式举例

Map<String, Integer> map = new HashMap<>();
map.put("apple", 1);
map.put("banana", 2);
map.put("orange", 3);

// 获取键集合，遍历键集合，通过get()方法获取对应的值
Set<String> keySet = map.keySet();
for (String key : keySet) {
   Integer value = map.get(key);
   System.out.println("key：" + key + "，value：" + value);
}

Map<String, Integer> map = new HashMap<>();
map.put("apple", 1);
map.put("banana", 2);
map.put("orange", 3);

// 获取值集合，遍历值集合
Collection<Integer> values = map.values();
for (Integer value : values) {
   System.out.println("value：" + value);
}

Map<String, Integer> map = new HashMap<>();
map.put("apple", 1);
map.put("banana", 2);
map.put("orange", 3);

// 获取键值对集合，遍历键值对集合，通过Entry的getKey()方法获取键，通过Entry的getValue()方法获取值
Set<Entry<String, Integer>> entrySet = map.entrySet();
for (Entry<String, Integer> entry : entrySet) {
   String key = entry.getKey();
   Integer value = entry.getValue();
   System.out.println("key：" + key + "，value：" + value);
}

Map<String, Integer> map = new HashMap<>();
map.put("apple", 1);
map.put("banana", 2);
map.put("orange", 3);

// 获取键流，遍历键流
map.keySet().stream().forEach(key -> System.out.println("key：" + key));

// 获取值流，遍历值流
map.values().stream().forEach(value -> System.out.println("value：" + value));

// 获取键值对流，遍历键值对流，通过Entry的getKey()方法获取键，通过Entry的getValue()方法获取值
map.entrySet().stream().forEach(entry -> System.out.println("key：" + entry.getKey() + "，value：" + entry.getValue()));

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
public class Base2 {
    /**
     *
     * @param args
     */
    public static void main(String[] args) {
        Map<String, Object> map = new HashMap<>();
        map.put("1", "张三");
        map.put("2", "李四");
        map.put("3", "王五");
        //方法一：使用keySet()方法将key放入set中
        Set<String> set = map.keySet();//先使用set得到map的所有key
        Iterator<String> it = set.iterator();//构造set的迭代器
        while (it.hasNext()) {
            String key = it.next();
            Object value = map.get(key);
            System.out.println("key" + key + "value" + value);
        }
        //方法二 ： 用增强for循环来代替 iterator
        Set<String> set1 = map.keySet();
        for (String key1 : set1) {
            Object value1 = map.get(key1);
            System.out.println("key" + key1 + "value" + value1);
            //方法三 ：将map的键值对用entrySet方法取出，再放入到set当中
            Set<Map.Entry<String, Object>> map1 = map.entrySet();
            for (Map.Entry<String, Object> maps :
                      map1) {
                String key2 = maps.getKey();
                Object Value2 = maps.getValue();
                System.out.println("key" + key2 + "value" + Value2);
            }
            //方法四
            Iterator iterator = map.entrySet().iterator();
            while (iterator.hasNext()){
                Map.Entry maps = ( Map.Entry)iterator.next();
                Object key = maps.getKey();
                Object value = maps.getValue();
                System.out.println("key" + key + "value" + value);
            }
        }
    }}