Java中的内部类 - 非静态变量错误 [英] Inner classes in Java - Non static variable error

问题描述

我还是新的java和我试图创建一个内部类，并调用main里面的方法。
但是编译错误说非静态变量 - 这不能从静态上下文引用

请帮助

  class Class1 {
 
 public static void main（String args []）{
 Class2 myObject = new Class2 
 myObject.newMethod（）; 
} 
 
 public class Class2 {
 public void newMethod（）{
 System.out.println（Second class）; 
} 
} 
} 
  

解决方案>

类需要引用 outer 类的实例才能构建。如果你的类在逻辑上不需要它，那么使用 static modifer使它只是一个嵌套类：

  public static class Class2 {
 public void newMethod（）{
 System.out.println（Second class）; 
} 
} 
  

编辑：创建 Class2 作为内部类，您可以使用类似：

  Class1 outer = new Class1（）; 
 Class2 myObject = outer.new Class2（）; 
  

或更简单：

  Class2 myObject = new Class1（）。new Class2（）; 
  

...除非您真的需要 ，将类作为一个嵌套类简单得多。

Im still new to java and i tried to create a inner class and call the method inside main. But theres a compilation error saying "Non static variable - This cannot be referenced from a static context"

Please help

class Class1{

    public static void main(String args []){
        Class2 myObject = new Class2();
        myObject.newMethod();
    }

    public class Class2{
        public void newMethod(){
            System.out.println("Second class");
        }
    }
}

解决方案

An inner class needs a reference to an instance of the outer class in order to be constructed. If your class doesn't logically need that, then use the static modifer to make it "just a nested class":

public static class Class2 {
    public void newMethod(){
        System.out.println("Second class");
    }
}

EDIT: To create an instance of Class2 as an inner class, you could use something like:

Class1 outer = new Class1();
Class2 myObject = outer.new Class2();

Or more briefly:

Class2 myObject = new Class1().new Class2();

... but unless you really want a reference to an enclosing instance, it's much simpler to make the class just a nested class.

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