Java測驗不工作需要if語句的幫助

Question

我正在Java中進行一個簡單的測驗，但是，我遇到了一些麻煩。

import java.util.Scanner; 
public class quiz { 
    public static void main(String[] args) { 
     Scanner keyboard = new Scanner(System.in); 
     String q1 = "London"; 
     String a1; 
     int q2 = 20; 
     int a2; 
     String q3 = "Java"; 
     String a3; 
     int score = 0; 

     System.out.println("What is the capital of England? "); 
     a1 = keyboard.next(); 
     if(a1 == q1) { 
      score + 1; 
      System.out.println("Correct!"); 
     } 
     else if { 
      System.out.println("WRONG!"); 
     } 

     System.out.println("What is 10 + 10?"); 
     a2 = keyboard.nextInt(); 
     if(a2 == q2) { 
      score + 1; 
      System.out.println("Correct!"); 
     } 
     else if { 
      System.out.println("WRONG"); 
     } 

     System.out.println("What langauge is kevin learning?"); 
     a3 = keyboard.next(); 
     if(a3 == q3) { 
      score + 1; 
      System.out.println("Correct!"); 
     } 
     else if { 
      System.out.println("WRONG"); 
     } 

     System.out.println("Your total marks were" score); 
    } 
} 

Answer 1

錯誤String比較：

if(a1 == q1) 

應該是：

if(a1.equals(q1)) 

同一故事：

if(a3 == q3) 

Answer 2

你必須使用他們的比較字符串方法==不比較字符串，而是對象在內存中的位置。 所以，相反的if(a1 == q1)使用if(a1.equals(q1))

編輯：這裏是workig代碼：

import java.util.Scanner; 

public class quiz { 
    public static void main(String[] args) { 
     Scanner keyboard = new Scanner(System.in); 
     String q1 = "London"; 
     String a1; 
     int q2 = 20; 
     int a2; 
     String q3 = "Java"; 
     String a3; 
     int score = 0; 

     System.out.println("What is the capital of England? "); 
     a1 = keyboard.next(); 
     if(a1.equals(q1)) { 
      score += 1; 
      System.out.println("Correct!"); 
     } 
     else { 
      System.out.println("WRONG!"); 
     } 

     System.out.println("What is 10 + 10?"); 
     a2 = keyboard.nextInt(); 
     if(a2 == q2) { 
      score += 1; 
      System.out.println("Correct!"); 
     } 
     else { 
      System.out.println("WRONG"); 
     } 

     System.out.println("What langauge is kevin learning?"); 
     a3 = keyboard.next(); 
     if(a3.equals(q3)) { 
     score += 1; 
      System.out.println("Correct!"); 
     } 
    else { 
      System.out.println("WRONG"); 
     } 

    System.out.println("Your total marks were" + score); 
    } 
}