for循环,增强for循环与Iterator的比较

先看看他们的写法

• 普通for循环

• 复制代码ArrayList<String> list = new ArrayList<>(); for (int i = 0; i < list.size(); i++) { String x = list.get(i); System.out.println(x); }

  1
  2
  3
  4
  5
  6
  ArrayList<String> list = new ArrayList<>();
  for (int i = 0; i < list.size(); i++) {
      String x = list.get(i);
      System.out.println(x);
  }
  

• 增强for循环

• 复制代码ArrayList<String> list = new ArrayList<>(); for (String s : list) { System.out.println(s); }

  1
  2
  3
  4
  5
  ArrayList<String> list = new ArrayList<>();
  for (String s : list) {
      System.out.println(s);
  }
  

• Iterator

• 复制代码ArrayList<String> list = new ArrayList<>(); Iterator<String> iterator = list.iterator(); while(iterator.hasNext()) { String string = iterator.next(); System.out.println(string); }

  1
  2
  3
  4
  5
  6
  7
  ArrayList<String> list = new ArrayList<>();
  Iterator<String> iterator = list.iterator();
  while(iterator.hasNext()) {
      String string = iterator.next();
      System.out.println(string);
  }
  

然后看看他们编译后生成的代码

• 普通for循环

  复制代码ArrayList var1 = new ArrayList(); for(int var2 = 0; var2 < var1.size(); ++var2) { String var3 = (String)var1.get(var2); System.out.println(var3); }

  1
  2
  3
  4
  5
  6
  7
  ArrayList var1 = new ArrayList();
  
  for(int var2 = 0; var2 < var1.size(); ++var2) {
      String var3 = (String)var1.get(var2);
      System.out.println(var3);
  }
  

• 增强for循环

• 复制代码ArrayList var1 = new ArrayList(); Iterator var2 = var1.iterator(); while(var2.hasNext()) { String var3 = (String)var2.next(); System.out.println(var3); }

  1
  2
  3
  4
  5
  6
  7
  8
  ArrayList var1 = new ArrayList();
  Iterator var2 = var1.iterator();
  
  while(var2.hasNext()) {
      String var3 = (String)var2.next();
      System.out.println(var3);
  }
  

• Iterator

• 复制代码ArrayList var1 = new ArrayList(); Iterator var2 = var1.iterator(); while(var2.hasNext()) { String var3 = (String)var2.next(); System.out.println(var3); }

  1
  2
  3
  4
  5
  6
  7
  8
  ArrayList var1 = new ArrayList();
  Iterator var2 = var1.iterator();
  
  while(var2.hasNext()) {
      String var3 = (String)var2.next();
      System.out.println(var3);
  }
  

  对,你没有看错,增强for循环的写法,编译后的文件跟Iterator写法编译后生成的文件是一样的,

由此可以得出,增强for循环就是简化了的Iterator的写法.

​ 增强for循环的适用范围:实现了Iterable接口的类都适用

举个简单的例子:

​ MyArray实现了Iterable接口

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
public class MyArray implements Iterable<Integer> {

    Integer[] o = new Integer[]{1, 2, 3, 4, 5, 6, 7};

    @Override
    public Iterator<Integer> iterator() {
        return new Iterator<Integer>() {
            int cursor = 0;

            @Override
            public boolean hasNext() {
                return cursor != o.length;
            }

            @Override
            public Integer next() {
                return o[cursor++];
            }
        };
    }

    @Override
    public void forEach(Consumer<? super Integer> action) {

    }

    @Override
    public Spliterator<Integer> spliterator() {
        return null;
    }
}

​ 使用

1
2
3
4
5
MyArray myArray = new MyArray();
for (Integer integer : myArray) {
    System.out.println(integer);
}

有一点需要注意一下,在多线程的情况下,一个使用增强for循环遍历的时候,另一个线程修改的时候会造成ConcurrentModificationException(并发修改异常)错误

最后

以上就是友好灰狼最近收集整理的关于for循环,增强for循环与Iterator的比较的全部内容，更多相关for循环,增强for循环与Iterator内容请搜索靠谱客的其他文章。