Java-其他逻辑 [英] Java - If Else Logic

问题描述

我很难理解为什么第二个字符串无法打印.即使我注释掉第三字符串"打印行，也没有输出.

I'm having a difficult time understanding why the second string does not print. Even if I comment out the "third string" print line, there is no output.

public class SecretMessage {
       public static void main (String [] args) {
            int aValue=4;
            if (aValue > 0){
                if (aValue == 0)
                System.out.print("first string   ");
        }
        else 
        System.out.println("second string   ");
        System.out.println("third string   ");
        }
    }

为什么不显示第二个字符串"?我认为else块下的所有内容都将执行，因此第二个和第三个字符串都应打印.

Why doesn't the "second string" print? I thought that anything under the else block would be executed, so both second and third string should be printed.

提前谢谢！

推荐答案

如果我们正确地缩进您的代码并写出(隐式)花括号，那么显然发生了什么:

If we indent your code properly and write the (implicit) braces, it becomes apparent what is going on:

public class SecretMessage {
    public static void main (String[] args) {
        int aValue = 4;
        if (aValue > 0){
            if (aValue == 0) {
                System.out.print("first string");
            }
        } else /* if (avalue <= 0) */ {
            System.out.println("second string");
        }
        System.out.println("third string");
    }
}

对于aValue = 4;，输入的是外部if(a > 0)，而不是内部的if(a == 0).因此，不会输入else.因此，只有System.out.println("third string");被执行.

With aValue = 4;, the outer if is entered (a > 0), but not the inner if (a == 0). Thus, the else is not entered. Thus only System.out.println("third string"); gets executed.

您的代码上有一些注释:

Some remarks on your code:

• 内部if不能输入.如果输入了外部if，则i为> 0，因此不能为== 0.
• 您使用System.out.print(...)和System.out.println(...).我有一种感觉，您想使用其中之一.为了提高可读性，您还可以忽略这些语句中的尾随空白.
• 数组括号([])应该直接跟随类型，没有空格(String [] args-> String[] args).

• The inner if can never be entered. If the outer if is entered, then i is > 0 and can therefore not be == 0.
• You use System.out.print(...) and System.out.println(...). I have a feeling that you want to use one or the other. For readability, you can also neglect the trailing blanks in those statements.
• the array-brackets ([]) should directly follow the type, without a space (String [] args -> String[] args).

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