需要帮助，让两个类互相帮助 [英] Need help to get two classes to assist each other

问题描述

我目前只是愚弄不同的类来测试它们如何一起工作，但我得到一个错误消息在NetBeans，我不能解决。这是我的代码：

class first_class.java

  public class first_class {
 
 private second_class state; 
 
 int test_tal = 2; 
 
 public void test（int n）{
 if（n> 2）{
 System.out.println（HELLO）; 
} 
 else {
 System.out.println（GOODBYE）; 
} 
} 
 
 public static void main（String [] args）{
 state.john（）; 
 TestingFunStuff.test（2）; 
 
} 
} 
  

class second_class

  public class second_class {
 
 first_class state; 
 
 public int john（）{
 if（state.test_tal == 2）{
 return 4; 
} 
 else {
 return 5; 
} 
} 
} 
  

显然我无法运行在我的主类中的方法john，因为非静态变量状态不能从静态上下文引用和方法test，因为非静态方法test（int）不能从静态上下文引用 p>

这是什么意思？

netbeans中显示的错误的屏幕截图： http://imageshack.us/photo/my-images/26/funstufffirstclassnetbe.png/

解决方案

这意味着 state 必须声明为静态成员要从静态方法使用它，或者您需要一个 first_class 的实例，您可以从中访问非静态成员。在后一种情况下，你需要提供一个getter方法（或使它公开，但是ew）。

此外， code> second_class ，所以在编译之后，你会得到一个 NullPointerException ：static或者是否需要一个实例访问实例方法。

---

我可能建议遵循Java命名约定，使用 camelCase 而不是 under_scores ，并用大写字母开头类名。

i'm currently just fooling around with different classes to test how they work together, but im getting an error message in NetBeans that i cant solve. Here's my code:

class first_class.java

public class first_class {

private second_class state;

int test_tal=2;

public void test (int n) {
    if (n>2) {
        System.out.println("HELLO");
    }
    else {
        System.out.println("GOODBYE");
    }
}

public static void main(String[] args) {
    state.john();
    TestingFunStuff.test(2);

}
}

class second_class

public class second_class {

first_class state; 

public int john () {
    if (state.test_tal==2) {
        return 4;
    }
    else {
        return 5;
    }
}
}

Apparently i can't run the method "john" in my main class, because "non static variable state cannot be referenced from a static context" and the method "test" because "non static method test(int) cannot be referenced from a static context".

What does this mean exactly?

Screenshot of the error shown in netbeans: http://imageshack.us/photo/my-images/26/funstufffirstclassnetbe.png/

解决方案

It means state must be declared as a static member if you're going to use it from a static method, or you need an instance of first_class from which you can access a non-static member. In the latter case, you'll need to provide a getter method (or make it public, but ew).

Also, you don't instantiate an instance of second_class, so after it compiles, you'll get a NullPointerException: static or not, there needs to be an instance to access an instance method.

---

I might recommend following Java naming conventions, use camelCase instead of under_scores, and start class names with upper-case letters.

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