我们可以覆盖Java中的构造函数，并且构造函数可以是私有的吗？ [英] Can we override a constructor in Java and can a constructor be private?

问题描述

我很感激这些问题的解释：

I would appreciate an explanation for these questions:

1. 我们可以覆盖 Java中的构造函数？


2. 构造函数可以是私有的吗？

1. Can we Override a constructor in Java?
2. Can a Constructor be private?

推荐答案

不，你不能覆盖构造函数。他们不是遗传的。但是，每个子类构造函数必须将 链接到子类或中的另一个构造函数到超类中的构造函数。例如：

No, you can't override a constructor. They're not inherited. However, each subclass constructor has to chain either to another constructor within the subclass or to a constructor in the superclass. So for example:

public class Superclass
{
    public Superclass(int x) {}

    public Superclass(String y) {}
}

public class Subclass extends Superclass
{
    public Subclass()
    {
        super(5); // chain to Superclass(int) constructor
    }
}

含义不被继承的构造函数是不能执行此操作：

The implication of constructors not being inherited is that you can't do this:

// Invalid
Subclass x = new Subclass("hello");

至于你的第二个问题，是的，构造函数可以是私有的。它仍然可以在类或任何封闭类中调用。这对于单身人士来说很常见：

As for your second question, yes, a constructor can be private. It can still be called within the class, or any enclosing class. This is common for things like singletons:

public class Singleton
{
    private static final Singleton instance = new Singleton();

    private Singleton()
    {
        // Prevent instantiation from the outside world (assuming this isn't
        // a nested class)
    }

    public static Singleton getInstance() {
        return instance;
    }
}

私人构造函数也用于防止任何实例化，如果你有一个只有静态方法的实用程序类。

Private constructors are also used to prevent any instantiation, if you have a utility class which just has static methods.

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