Starting from JDK1.5, a new function Foreach has been added, which is an abbreviation for a for loop to traverse data. The keyword used is still for, but the parameter format is different. Its detailed usage is:
for(Type e:collection){ //对变量e的使用}
Parameter description:
e: Its type Type is the type of the element value in the collection or array. This parameter is in the collection or array collection. of an element.
collections: The collection or array to be traversed, or it can be an iterator.
Use parameter e in the loop body, which is the element value that foreach obtains from the collection or array and iterator. The element value is traversed from beginning to end.
Specific example:
//必须导入util下面的这两个包:ArrayList,List; import java.util.ArrayList; import java.util.List; public class Foreach { public static void main(String[] arg){ List<String> list = new ArrayList<String>(); //创建List集合 list.add("abc"); //初始化list集合 list.add("def"); list.add("ghi"); list.add("jkl"); list.add("mno"); list.add("pqr"); System.out.print("Foreach遍历集合: \n\t"); for(String string:list){ //遍历List集合 System.out.print(string); //输出集合的元素值 } System.out.println(); String[] strs = new String[list.size()]; list.toArray(strs); //创建数组 System.out.println("Foreach遍历数组:\n\t"); for(String string: strs){ //遍历数组 System.out.print(string); //输出数组元素值 } } }
Summary:
Previous versions of JDK used for loops to traverse collections, arrays and iterators. This requires creating index variables, conditional expressions, which clutters the code and increases the chance of errors. And in each loop, the index variable or iterator will appear three times, giving two chances for error. And there will be some performance losses, its performance is slightly behind the foreach loop. Therefore, for traversing data collections, it is recommended to use a Foreach loop.
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