为什么Java静态方法可以调用构造函数，但不能引用它呢? [英] Why can a Java static method call a constructor, but not refer to this?

问题描述

我的假设:

1. 静态方法不能调用非静态方法.
2. 构造函数是一种方法，没有返回类型.

1. Static method cannot cannot call non-static methods.
2. Constructors are kind of a method with no return type.

给出此示例...

    public class Main {
        public static void main(String[] args) {
            Main p = new Main();  // constructor call
            k();  // [implicit] `this` reference
        }

        protected Main() {
            System.out.print("1234");
        }

        protected void k() {
        }
    }

• 此行打印1234: Main p = new Main()
• 此行引发异常: k()

示例代码为什么要做这两件事?他们不与我的上述假设相抵触吗?我的假设正确吗?

推荐答案

1-静态方法不能调用非静态方法.

1 - Static method cannot cannot call non-static methods.

可以，但是需要一个对象来调用该方法.

在静态方法中，没有可用的 this 引用，因此， foo()(等效于 this.foo())是非法的.

In a static method, there's no this reference available, so foo() (which is equivalent to this.foo()) is illegal.

2-构造函数是一种没有返回类型的方法.

2 - Constructors are kind of a method with no return type.

如果应该将它们与方法相比 会说构造函数更接近于非静态方法(因为在构造函数中确实存在 this 引用).

If they should be compared to methods, I would say constructors are closer to non-static methods (since there is indeed a this reference inside a constructor).

鉴于此观点，您应该清楚为什么静态方法可以毫无问题地调用构造函数.

Given this view, it should be clear to you why a static method can call a constructor without any problems.

所以，总结一下:

Main p = new Main();

可以，因为 new Main()不依赖任何现有对象.

is okay, since new Main() does not rely on any existing object.

k();

不好，因为它等同于 this.k()，并且 this 在您的(静态)主方法中不可用.

is not okay since it is equivalent to this.k() and this is not available in your (static) main method.

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