在条件句中使用布尔true和false

Question

public class FavNum {

    public static void isEven(int x){
       boolean b;
       if (x%2==0) {
          b=true;
       }else{
          b=false;
       }
    }

    public static void isSingle(int x){
       boolean b;
       if (x > 0 && x < 10){
          b=true;        
       }else{
          b=false;
          JOptionPane.showMessageDialog(null, "Your favorite number is not a single digit!");        
       }
    }

    public static void all(int x){
       isEven (x);
       //What should I add here to use isEven and isSingle in conditionals? 
       //For example, I want to say something like if isEven and isSingle are true, then say this. 
       //Or if isEven is true and isSingle is not, say this.  But I don't know how to properly write those conditionals.
    }

    public static void main(String[] args) {
       int x = Integer.parseInt(JOptionPane.showInputDialog(null, "What is your favorite number?"));        
    }    
}

这方面的指示如下”

• 创建名为FavoriteNumber的新项目

到目前为止，我已经完成了前4项任务。我在第五颗子弹上遇到了麻烦（我想我还不完全理解）。我试图通过创建一个名为all的新方法来实现这一点，我计划在其中调用isSingle和isEven，并使用if-else语句来比较它们并相应地返回消息。但我被卡住了，在我上面的代码中留下了解释我的问题的注释。

有人能帮我完成这个任务吗？或者至少给我指出正确的方向？

谢谢你！

Answer 1

看起来你已经弄清楚了算法部分从你的方法中，你需要返回布尔值而不是无效

 public static boolean isEven(int x){
   return (x % 2) == 0;
 }

Answer 2

public class Joption {

    // declared outside so easier to be accessed by other methods in the class
    private static int x;

    // is the number passed into this method even?
    private static boolean isEven(int x) {
        if (x % 2 == 0) {
            return true;
        }
        return false;
    }

    // is the number passed into this method single?
    private static boolean isSingle(int x) {
        if (x >= 0 || x < 10) {
            return true;
        }
        return false;
    }

    // is the number passed in even AND single?
    // notice how the number passed in flows into the two methods you just created. Their returns help you determine if they are even AND single.
    private static void isEvenAndSingle(int x) {
        if (isEven(x) && isSingle(x)) {
            JOptionPane.showMessageDialog(null, x + "is Even and Single!");
        }
    }

    // same as above method but now it's checking to see if it's even and NOT single.
    private static void isEvenAndNotSingle(int x) {
        if (isEven(x) && !(isSingle(x))) {
            JOptionPane.showMessageDialog(null, x + "is Even but NOT single!");
        }
    }

    // your main running method
    // here you actually need to call the isEvenAndSingle() and isEvenAndNotSingle() methods with the retrieved x value from the JOptionPane so that you can actually print the appropriate messages in the responding JOptionPane
    public static void main(String[] args) {
        x = Integer.parseInt(JOptionPane.showInputDialog(null, "What is your favorite number?"));
        isEvenAndSingle(x);
        isEvenAndNotSingle(x);
    }

}

如前所述，您的问题在于您从JOptionPane中检索值的方式。您将其作为int获取。但您将其作为布尔值传递到您的方法中。您实际上需要做的是将值作为int传递（请参阅is0022（）和isSing（）方法）并让它们返回一个布尔值。

然后要求您创建与您刚刚创建的两个方法的比较。一个用于如果数字是偶数和单个，另一个用于如果数字是偶数和非单个。

我用注释对代码进行了注释，以帮助您更好地理解！祝你未来的java编码好运！：）

Answer 3

你在比较布尔值和数字：

boolean x;

 if (x%2==0) {   //Error here
    b=true;
}

 if (x > 0 && x < 10){     //Error here
       b=true;

你不能那样做。

如果x是true或false，则无法检查其是否大于0，也无法对其进行算术运算。