遍历Map集合的四种方法

Myth丶恋晨 2022-05-18 09:42 218阅读 0赞

JSP页面中经常会出现遍历Map集合的情况，有以下四种方法：

public static void main(String[] args) {
    		Map<Person, String> map = new HashMap<>();
    		map.put(new Person("Ham", 33), "Britain");
    		map.put(new Person("Bot", 29), "Finland");
    		map.put(new Person("Vet", 31), "Germany");
    		map.put(new Person("Rai", 39), "Finland");
    		keySetIterator(map);
    		keySetForeach(map);
    		entrySetIterator(map);
    		entrySetForeach(map);
    	}
    
    	// keySet方法的迭代器遍历
    	public static <K, V> void keySetIterator(Map<K, V> map) {
    		Set<K> keySet = map.keySet();
    		Iterator<K> it = keySet.iterator();
    		while (it.hasNext()) {
    			K next = it.next();
    			System.out.println(next + "::" + map.get(next));
    		}
    	}
    
    	// keySet方法的foreach遍历
    	public static <K, V> void keySetForeach(Map<K, V> map) {
    		Set<K> keySet = map.keySet();
    		for (K k : keySet) {
    			System.out.println(k + "::" + map.get(k));
    		}
    	}
    
    	// entrySet方法的迭代器遍历
    	public static <K, V> void entrySetIterator(Map<K, V> map) {
    		Set<Entry<K, V>> entrySet = map.entrySet();
    		Iterator<Entry<K, V>> it = entrySet.iterator();
    		while (it.hasNext()) {
    			Entry<K, V> next = it.next();
    			K key = next.getKey();
    			V value = next.getValue();
    			System.out.println(key + "::" + value);
    		}
    	}
    
    	// entrySet方法的foreach遍历
    	public static <K, V> void entrySetForeach(Map<K, V> map) {
    		Set<Entry<K, V>> entrySet = map.entrySet();
    		for (Entry<K, V> entry : entrySet) {
    			K key = entry.getKey();
    			V value = entry.getValue();
    			System.out.println(key + "::" + value);
    		}
    	}

其中entrySet方法遍历是JSTL的foreach遍历使用的方法，务必牢记