System.out.println 不打印没有参数的行？

Question

public class Test2 {
    public static void mystery(int x, int y, boolean b, String s) {
        System.out.println(x*3 + "..." + x/y);
        if (b)
            System.out.println("yes");
        else
            System.out.println("no");
        for (int i = 2; i <= 5; i++)
            System.out.print(2*i);
        System.out.println();
        System.out.println((double)(y/x));
        System.out.println(s.substring(3,7));
     } // end mystery

     public static void main(String[] args) {
         mystery(7,3,true,"freezing");
     }
}

I'm a little confused and I think I'm missing something. How come the output of the for loop in this code is 46810? Shouldn't there be a line in between each of the numbers?

Answer 1

It appears to me that you wanted your loop to look like this:

for (int i = 2; i <= 5; i++)
 System.out.print(2*i);
 System.out.println();

But the for only applies to the first statement. To include multiple statements in the loop, you need to enclose the loop body in curly braces:

for (int i = 2; i <= 5; i++) {
 System.out.print(2*i);
 System.out.println();
}

It's best to always use curly braces when writing a for loop, and also while , do , if , and else , even though the language allows you to have a body of just one statement without the curly braces. For example:

 if (b) {
     System.out.println("yes");
 } else {
     System.out.println("no");
 }

Answer 2

Not with System.out.print(2 * i); . For the output you seem to expect change it to,

System.out.println(2 * i);

or add braces to your for loop like,

for (int i = 2; i <= 5; i++){
    System.out.print(2*i);
    System.out.println();
}

Java loops aren't controlled by indentation, you need braces to contain more than one line.

Answer 3

Try this:

for (int i = 2; i <= 5; i++)
{
    System.out.print(2*i);
    System.out.println();
    System.out.println((double)(y/x));
    System.out.println(s.substring(3,7));
}

When you are using the for loop then it is recommended to put the code inside it in the curly braces {} .

Answer 4

for 循环逻辑必须包含在{}