負數不被識別

Question

import java.util.Scanner; 

public class HelloWorld { 
    public static void main(String[] args) { 
     // Prints "Hello, World" in the terminal window. 

     Scanner quest = new Scanner(System.in);enter code here 
     System.out.println("How old are you?: "); 
     int num = quest.nextInt(); 

     if (num <= 12){ 
     System.out.println("You are too young to be on the computer!!!!"); 
     } else if (num >=13 && num <= 17){ 
     System.out.println("Welcome young teen"); 
     } else if (17 < num && num <= 60){ 
     System.out.println("Welcome adult"); 
     } else if (60 < num){ 
     System.out.println("Welcome senior citizen!!"); 
     } else{ 
     System.out.println("Invalid age."); 
     } 

    } 
} 

當我輸入一個負數時，它只屬於「你太年輕了，不能在電腦上!!!!」而不是顯示「無效的年齡」。我試圖改變條件，但它似乎沒有工作。

Answer 1

由於負數小於12，你可以通過測試負值，依靠先前免除了您&&檢查，檢查的條件簡化您的if-else塊鏈。 Like，

int num = quest.nextInt(); 
if (num < 0) { // <-- negative values. 
    System.out.println("Invalid age."); 
} else if (num <= 12) { // <-- (0, 12) 
    System.out.println("You are too young to be on the computer!!!!"); 
} else if (num <= 17) { // <-- (13, 17) 
    System.out.println("Welcome young teen"); 
} else if (num <= 60) { // <-- (18, 60) 
    System.out.println("Welcome adult"); 
} else { // <-- greater than 60 
    System.out.println("Welcome senior citizen!!"); 
} 

Answer 2

您應該已將其作爲if(Condition) { //Code }聲明的第一條件。那麼我做了一個代碼運行，並對代碼做了一些調整。

import java.util.Scanner; 

public class HelloWorld { 
    public static void main(String[] args) { 
     // Prints "Hello, World" in the terminal window. 

     Scanner quest = new Scanner(System.in); //enter code here 
     System.out.println("How old are you?: "); 
     int num = quest.nextInt(); 

     if (num <= 0) { 
      System.out.println("Invalid age."); 
     } else if (num <= 12){ 
     System.out.println("You are too young to be on the computer!!!!"); 
     } else if (num >=13 && num <= 17){ 
     System.out.println("Welcome young teen"); 
     } else if (17 < num && num <= 60){ 
     System.out.println("Welcome adult"); 
     } else if (60 < num){ 
     System.out.println("Welcome senior citizen!!"); 
     } 
    } 
}