Java条件语句（足够简单）

Question

我的程序是告诉输入的一年是否是符合这些要求的闰年：

a型年：2011年不是闰年。

a型年：2012年是闰年。

类型a年：1800年该年不是闰年。

import java.util.Scanner;

public class LeapYear {

    public static void main(String[] args) {
        Scanner reader = new Scanner(System.in);

        System.out.println(" Type a year ");
        int number = Integer.parseInt(reader.nextLine());

        if (number % 4 == 0 ) {
            System.out.println(" This is a leap year");
        } else if (number % 100 == 0 && number % 400 == 0) {
            System.out.println(" This is a leap year ");
        } else {
            System.out.println( "This is not a leap year");
        } 
    }
}  

Answer 1

考虑输入年份100时会发生什么。100%4==0为true，因此代码输出该年为闰年。问题是，100%100==0也是true，但是代码永远不会到达这一行，也不会检查100%400==0是否是true。

您在检查所有条件之前就打印出了结果！

更改if else的结构。

方括号{和}除其他外，位置不对。将括号放在我所做的位置是Java标准的一部分，它使代码更容易阅读、理解和调试。（这也使得识别它们丢失时更容易。）

您的代码应该如下所示：

// Pay attention to a few things here. It checks if it is divisible by 4
// since every leap year must be divisible by 4. If it is,
// it checks if it is divisible by 100. If it is, it must also
// be divisible by 400, or it is not a leap year. So, if it is divisible
// by 100 and NOT divisible by 400, it is not a leap year. If it isn't 
// divisible by 100, control flows to the else statement, and since we
// already tested number % 4 we know it is a leap year.
// Pay special attention to where I located my { and }, this is the 
// standard way to do it in java, it makes your code readable by others.

if(number % 4 == 0) {
    if((number % 100 == 0) && !(number % 400 == 0)) { // NOTE THE ! OPERATOR HERE
        System.out.println("The year is NOT a leap year.");
    } else {
        System.our.println("The year is a leap year.");
    }
} else {
    System.out.println("The year is NOT a leap year");
}