为什么不能在 Java 中将类声明为静态类? [英] Why are you not able to declare a class as static in Java?

问题描述

为什么不能在 Java 中将类声明为静态类?

Why are you not able to declare a class as static in Java?

推荐答案

只有嵌套类可以是静态的.通过这样做，您可以在没有外部类实例的情况下使用嵌套类.

Only nested classes can be static. By doing so you can use the nested class without having an instance of the outer class.

class OuterClass {
    public static class StaticNestedClass {
    }

    public class InnerClass {
    }

    public InnerClass getAnInnerClass() {
        return new InnerClass();
    }

    //This method doesn't work
    public static InnerClass getAnInnerClassStatically() {
        return new InnerClass();
    }
}

class OtherClass {
    //Use of a static nested class:
    private OuterClass.StaticNestedClass staticNestedClass = new OuterClass.StaticNestedClass();

    //Doesn't work
    private OuterClass.InnerClass innerClass = new OuterClass.InnerClass();

    //Use of an inner class:
    private OuterClass outerclass= new OuterClass();
    private OuterClass.InnerClass innerClass2 = outerclass.getAnInnerClass();
    private OuterClass.InnerClass innerClass3 = outerclass.new InnerClass();
}

来源:

• 关于嵌套类的 Oracle 教程

关于同一主题:

• Java:静态与非静态内部类
• Java 内部类和静态嵌套类

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