集合的周遊

集合的周遊方式

1.map集合的周遊

public class HashMapDemo {
	public static void main(String[] args) {

		// 建立集合對象
		HashMap<String, Integer> hm = new HashMap<>();

		hm.put("關羽", 30);
		hm.put("張飛", 28);
		hm.put("趙雲", 27);
		hm.put("馬超", 26);
		hm.put("黃忠", 50);

		// 1.鍵找值
		Set<String> set = hm.keySet();// {"關羽" ,"張飛" , "趙雲" ,"馬超" ,"黃忠"}

		for (String key : set) {
			int value = hm.get(key);
			System.out.println(key + "---" + value);
		}
		
		System.out.println("--------------");
		
		// 2.擷取鍵值對對象集合, 在擷取建和值
		Set<Entry<String, Integer>> set2 = hm.entrySet();
		
		for(Entry<String, Integer> entry : set2){
			String key = entry.getKey();
			Integer value = entry.getValue();
			System.out.println(key + "---" + value);
		}
		
		System.out.println("--------------");
		
		// 3.疊代器
		Set<String> set3 = hm.keySet();// {"關羽" ,"張飛" , "趙雲" ,"馬超" ,"黃忠"}

		Iterator<String> it = set3.iterator();
		while(it.hasNext()){
			String key = it.next();
			Integer value = hm.get(key);
			System.out.println(key + "---" + value);
		}

	}

}
           

2.collection集合的周遊 : 疊代器 &增強for

public class CollectionDemo2 {
	public static void main(String[] args) {
		// 建立集合對象
		Collection<String> c = new ArrayList<>();
		
		// 添加元素
		c.add("迪麗熱巴");
		c.add("古力娜紮");
		c.add("馬爾紮哈");
		
		// 1.疊代器 , 多态
		Iterator<String> it = c.iterator();
		while(it.hasNext()){
			String s = it.next();
			System.out.println(s);
		}
		System.out.println("-----------");
		
		// 2.增強for
		for(String s : c){
			System.out.println(s);
		}
		
	}

}
           

3. list 周遊方式：疊代器，增強for，普通for

public class ListDemo1 {
	public static void main(String[] args) {
		// 建立集合對象
		List<String> list = new ArrayList<>();

		// 添加元素
		list.add("迪麗熱巴");
		list.add("古力娜紮");
		list.add("馬爾紮哈");

		// 1.疊代器
		Iterator<String> it = list.iterator();
		while (it.hasNext()) {
			String s = it.next();
			System.out.println(s);
		}

		System.out.println("-------------");

		//2. 增強for
		for (String s : list) {
			System.out.println(s);
		}

		System.out.println("-------------");

		//3. 普通for循環
		for (int i = 0; i < list.size(); i++) {
			String s = list.get(i);
			System.out.println(s);
		}

	}

}