For-Each loop
The For-Each loop is also called an enhanced for loop, or a foreach loop.
For-Each loop is a new feature of JDK5.0 (other new features such as generics, autoboxing, etc.).
The addition of For-Each loop simplifies collection traversal.
The syntax is as follows:
for(type element: array) { System.out.println(element); }
Example
You can directly look at the code for its basic use:
The code first compares the two A for loop; then implemented an enhanced for loop to traverse a two-dimensional array; and finally used three methods to traverse a List collection.
import java.util.ArrayList; import java.util.Iterator; import java.util.List; public class ForeachTest { public static void main(String[] args) { int[] arr = {1, 2, 3, 4, 5}; System.out.println("----------旧方式遍历------------"); //旧式方式 for(int i=0; i<arr.length; i++) { System.out.println(arr[i]); } System.out.println("---------新方式遍历-------------"); //新式写法,增强的for循环 for(int element:arr) { System.out.println(element); } System.out.println("---------遍历二维数组-------------"); //遍历二维数组 int[][] arr2 = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}} ; for(int[] row : arr2) { for(int element : row) { System.out.println(element); } } //以三种方式遍历集合List List<String> list = new ArrayList<String>(); list.add("a"); list.add("b"); list.add("c"); System.out.println("----------方式1-----------"); //第一种方式,普通for循环 for(int i = 0; i < list.size(); i++) { System.out.println(list.get(i)); } System.out.println("----------方式2-----------"); //第二种方式,使用迭代器 for(Iterator<String> iter = list.iterator(); iter.hasNext();) { System.out.println(iter.next()); } System.out.println("----------方式3-----------"); //第三种方式,使用增强型的for循环 for(String str: list) { System.out.println(str); } } }
Disadvantages of For-Each loop: index information is lost.
When traversing a collection or array, if you need to access the subscript of the collection or array, it is better to use the old-style way to implement the loop or traversal instead of using the enhanced for loop, because it loses the subscript information.
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