找不到符號：Java

Question

對不起，如果這是一個奇怪的問題，但我剛剛開始OOP，並遇到了一個簡單的菜單驅動的數學程序，我應該做的這個問題。我清除了編譯器給我的所有錯誤，但現在它給了我大約14個新錯誤，其中大部分被描述爲'找不到符號'。這裏是我的代碼：

import java.util.Scanner; 


public class MathMenu 
{ 


//MENU METHOD 
private static void menu(String args[]) 
{ 
int choice; 

System.out.printf("Enter '1' to add"); 
System.out.printf("Enter '2' to subtract"); 
System.out.printf("Enter '3' to exit"); 

System.out.printf("\nPlease enter your choice: "); 


choice=input.nextInt(); 

if (choice==1) 
sum(n,m); 

if (choice==2) 
dif(n,m); 

else if(choice==3) 
return; 

} 



//SUM 
private static int sum(int a, int b) 
{ 
return n+m; 
} 


//DIFFERENCE 
private static int dif(int a, int b) 
{ 
if(n<m) 
return m-n; 

else 
return n-m; 
} 





public static void main(String args[]) 
{ 


int n=15; 
int m=8; 

Scanner input = new Scanner(System.in); 

menu(); 

} 


} 

，這裏是新的編譯器輸出：

Microsoft Windows [Version 6.1.7601] 
Copyright (c) 2009 Microsoft Corporation. All rights reserved. 

C:\Users\Shahraiz Tabassam>cd c:\java\bin 

c:\java\bin>javac MathMenu.java 
MathMenu.java:7: error: no suitable constructor found for Scanner() 
private static Scanner input = new Scanner(); 
          ^
    constructor Scanner.Scanner(ReadableByteChannel,String) is not applicable 
     (actual and formal argument lists differ in length) 
    constructor Scanner.Scanner(ReadableByteChannel) is not applicable 
     (actual and formal argument lists differ in length) 
    constructor Scanner.Scanner(String) is not applicable 
     (actual and formal argument lists differ in length) 
    constructor Scanner.Scanner(Path,Charset) is not applicable 
     (actual and formal argument lists differ in length) 
    constructor Scanner.Scanner(Path,String) is not applicable 
     (actual and formal argument lists differ in length) 
    constructor Scanner.Scanner(Path) is not applicable 
     (actual and formal argument lists differ in length) 
    constructor Scanner.Scanner(File,CharsetDecoder) is not applicable 
     (actual and formal argument lists differ in length) 
    constructor Scanner.Scanner(File,String) is not applicable 
     (actual and formal argument lists differ in length) 
    constructor Scanner.Scanner(File) is not applicable 
     (actual and formal argument lists differ in length) 
    constructor Scanner.Scanner(InputStream,String) is not applicable 
     (actual and formal argument lists differ in length) 
    constructor Scanner.Scanner(InputStream) is not applicable 
     (actual and formal argument lists differ in length) 
    constructor Scanner.Scanner(Readable) is not applicable 
     (actual and formal argument lists differ in length) 
    constructor Scanner.Scanner(Readable,Pattern) is not applicable 
     (actual and formal argument lists differ in length) 
MathMenu.java:64: error: method menu in class MathMenu cannot be applied to give 
n types; 
menu(); 
^ 
    required: String[] 
    found: no arguments 
    reason: actual and formal argument lists differ in length 
2 errors 

c:\java\bin> 

Answer 1

您從未定義過您的input變異在menu方法的身體。嘗試在menu方法內添加Scanner input = new Scanner(System.in)。簡單地定義main中的變量不是給menu訪問它。如果你想避免創建Scanner實例多次，你可以不喜歡

import java.util.Scanner; 

public class MathMenu { 
    private static Scanner input = new Scanner(System.in); 
    ... 
} 

那麼你可以使用所有的你的方法input。

---

編輯：我只是注意到了 m和 n類似的東西：你必須在正在使用他們的方法中定義它們，或讓他們 static領域。如果這取決於我，我會這樣做：

import java.util.Scanner; 

public class MathMenu { 
    private static Scanner input = new Scanner(System.in); 
    private static int n = 15; 
    private static int m = 8; 

    // ... 
    // your other methods unchanged 
    // ... 

    public static void main(String[] args) { 
     menu(args); // or just "menu()" if you remove the arguments from the menu method declaration. 
    } 
} 

Answer 2

您的所有功能得到命名一個& b，但論點ň&米工作。改變其中之一。例如：

private static int sum(int n, int m) 
{ 
    return n+m; 
} 

Answer 3

你沒有在你的程序中定義input，但調用

choice=input.nextInt();

假設你想從用戶那裏得到輸入，你需要有

Scanner input = new Scanner(System.in) 

權之前choice=input.nextInt();