Set 遍历的四种方法

Set 遍历的四种方法

1. 增强for
2. 迭代器
3. toArray 转化为数组
4. stream 流

其中 Stream 查询速度最慢

List除了以上前三种还有一个get()方法可以遍历

set四种遍历代码如下：

public class SetTest {

public static void main(String[] args) {
       HashSet<String> set = new HashSet<>();

       set.add("hello");
       set.add("world");
       set.add("qiuqiu");

       long currentTimeMillis = System.currentTimeMillis();
       //1.增强for
       for (String s : set) {
           System.out.println(s);
       }
       System.out.println(System.currentTimeMillis() - currentTimeMillis);
       //2.迭代器
       currentTimeMillis = System.currentTimeMillis();
       Iterator<String> iterator = set.iterator();
       while (iterator.hasNext()){
           String next = iterator.next();
           System.out.println(next);
       }
       System.out.println(System.currentTimeMillis() - currentTimeMillis);

       //3.toArray(),转换为数组
       currentTimeMillis = System.currentTimeMillis();
       Object[] array = set.toArray();
       for (int i = 0; i < array.length; i++) {
           System.out.println(array[i]);
       }
       System.out.println(System.currentTimeMillis() - currentTimeMillis);

       //4.stream;流
       currentTimeMillis = System.currentTimeMillis();
      set.forEach(s -> {
          System.out.println(s);
      });
       System.out.println(System.currentTimeMillis() - currentTimeMillis);
   }
}



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