Question

所以我有这个代码并打印出来：

import java.util.*;

public class Reverse_Copy {

    public static void main(String[] args){

        //create an array and covert to list
        Character[] ray = {'p','w','n'};
        List<Character> l = new ArrayList<Character>(Arrays.asList(ray));
        System.out.println("List is: ");
        output(l);

        //reverse and print out the list
        Collections.reverse(l);
        System.out.println("After reverse: ");
        output(l);

        //create a new array and a new list
        Character[] newray = new Character[3];
        List<Character> listCopy = new ArrayList<Character>(Arrays.asList(newray));

        //copy contens of list l into list listCopy
        Collections.copy(listCopy, l);
        System.out.println("Copy of list: ");
        output(listCopy);

        //fill collection with crap
        Collections.fill(l,'X');
        System.out.println("After filling the list: ");
        output(l);

    }

    private static void output(List<Character> thelist){

        for(Character thing: thelist)
            System.out.printf("%s ", thing);
            System.out.println();


    }

}

这是印刷品：

List is: 
p w n 
After reverse: 
n w p 
Copy of list: 
n w p

这是与enhanced for loops括号相同的代码。

    import java.util.*;

    public class Reverse_Copy {

    public static void main(String[] args){

        //create an array and covert to list
        Character[] ray = {'p','w','n'};
        List<Character> l = new ArrayList<Character>(Arrays.asList(ray));
        System.out.println("List is: ");
        output(l);

        //reverse and print out the list
        Collections.reverse(l);
        System.out.println("After reverse: ");
        output(l);

        //create a new array and a new list
        Character[] newray = new Character[3];
        List<Character> listCopy = new ArrayList<Character>(Arrays.asList(newray));

        //copy contens of list l into list listCopy
        Collections.copy(listCopy, l);
        System.out.println("Copy of list: ");
        output(listCopy);

        //fill collection with crap
        Collections.fill(l,'X');
        System.out.println("After filling the list: ");
        output(l);

    }

    private static void output(List<Character> thelist){

        for(Character thing: thelist){
            System.out.printf("%s ", thing);
            System.out.println();
        }

    }

}

这是印刷品：

List is: 
p 
w 
n 
After reverse: 
n 
w 
p 
Copy of list: 
n 
w 
p 
After filling the list: 
X 
X 
X

我发现这非常奇特，简单的括号与打印的方式有什么关系？有关为什么会发生这种情况的任何想法？如果你不相信我，你可以自己测试一下。我发现没有任何理由可以解决这个问题。非常奇怪。

编辑：重复网站中的答案仅证明它不会改变任何内容。证明如何添加花括号会改变事物而不是保持一致。

Answer 1

当省略for循环中的括号时，只执行第一行：

 for(Character thing: thelist)
        System.out.printf("%s ", thing);
        System.out.println();

哪个会为printf中的每个元素执行thelist行，然后只执行一次println。不要让缩进愚弄你。

和

 for(Character thing: thelist){
    System.out.printf("%s ", thing);
    System.out.println();
}

这将为printf中的每个元素执行println行和thelist行。

{}格式不同？格式化困境

1 个答案: