Java中for的几种常见形式

1.For loop using index.

for (int i = 0; i < arr.length; i++) {     type var = arr[i];    body-of-loop}复制代码

2.Loop using explicit iterator.

for (Iterator
    
      iter = coll.iterator(); iter.hasNext(); ) {    type var = iter.next();    body-of-loop}复制代码
    

3.Foreach loop over all elements in arr.

for (type var : coll) {    body-of-loop}复制代码

For循环用来处理哪些数据结构

1.数组

int[] a = {1,2,3,4,5,6};int[] b = new int[]{1,2,3,4,5,6};int[] c = new int[6];for (int i = 0; i < a.length; i++) {    System.out.println(i);}for (int i : a) {    System.out.println(i);}复制代码

2.实现了java.util.Iterator的类

import java.util.Iterator;public class IterableTest
    
      implements Iterable
     
       {    public static void main(String[] args) {        IterableTest
      
        integers = new IterableTest
       
        ();        for (Integer integer : integers) {            System.out.println(integer);        }    }    @Override    public Iterator
        
          iterator() {        return new Iterator() {            @Override            public boolean hasNext() {                //...                return false;            }            @Override            public Object next() {                //...                return null;            }            @Override            public void remove() {                //...            }        };    }}复制代码
        
       
      
     
    

普通for遍历和增强for的一些区别

增强的for循环的底层使用迭代器来实现，所以它就与普通for循环有一些差异

1. 增强for使用增强for循环的时候不能使用集合删除集合中的元素；
2. 增强for循环不能使用迭代器中的方法，例如remove()方法删除元素；
3. 与普通for循环的区别：增强For循环有遍历对象，普通for循环没有遍历对象;

对于实现了RandomAccess接口的集合类，推荐使用普通for，这种方式faster than Iterator.next

The RandomAccess interface identifies that a particular java.util.List implementation has fast random access. (A more accurate name for the interface would have been "FastRandomAccess.") This interface tries to define an imprecise concept: what exactly is fast? The documentation provides a simple guide: if repeated access using the List.get( ) method is faster than repeated access using the Iterator.next( ) method, then the List has fast random access. The two types of access are shown in the following code examples.

参考资料