Java中的静态类

问题描述

java中是否有类似静态类的内容？

Is there anything like static class in java?

此类的含义是什么？静态类的所有方法都需要 static 吗？

What is the meaning of such a class. Do all the methods of the static class need to be static too?

是否需要反过来，如果一个类包含所有静态方法，那么该类是否也应该是静态的？

Is it required the other way round, that if a class contains all the static methods, shall the class be static too?

什么是静态类适合的？

推荐答案

Java有静态嵌套类，但听起来你正在寻找一个顶级静态类。 Java无法使顶级类静态，但您可以模拟这样的静态类：

Java has static nested classes but it sounds like you're looking for a top-level static class. Java has no way of making a top-level class static but you can simulate a static class like this:

• 声明您的类 final - 防止扩展类，因为扩展静态类是没有意义的


• 使构造函数 private - 防止客户端代码实例化，因为实例化静态类是没有意义的


• 使所有类的成员和函数 static - 由于无法实例化类，因此无法调用实例方法或访问实例字段


• 请注意，编译器不会阻止您声明实例（非静态）成员。只有在您尝试调用实例成员时才会出现此问题

• Declare your class final - Prevents extension of the class since extending a static class makes no sense
• Make the constructor private - Prevents instantiation by client code as it makes no sense to instantiate a static class
• Make all the members and functions of the class static - Since the class cannot be instantiated no instance methods can be called or instance fields accessed
• Note that the compiler will not prevent you from declaring an instance (non-static) member. The issue will only show up if you attempt to call the instance member

根据上述建议的简单示例：

Simple example per suggestions from above:

public class TestMyStaticClass {
     public static void main(String []args){
        MyStaticClass.setMyStaticMember(5);
        System.out.println("Static value: " + MyStaticClass.getMyStaticMember());
        System.out.println("Value squared: " + MyStaticClass.squareMyStaticMember());
        // MyStaticClass x = new MyStaticClass(); // results in compile time error
     }
}

// A top-level Java class mimicking static class behavior
public final class MyStaticClass {
    private MyStaticClass () { // private constructor
        myStaticMember = 1;
    }
    private static int myStaticMember;
    public static void setMyStaticMember(int val) {
        myStaticMember = val;
    }
    public static int getMyStaticMember() {
        return myStaticMember;
    }
    public static int squareMyStaticMember() {
        return myStaticMember * myStaticMember;
    }
}

静态类有什么用？静态类的一个好用途是定义一次性，实用程序和/或库类，其中实例化没有意义。一个很好的例子是Math类，它包含一些数学常量，如PI和E，只是提供数学计算。在这种情况下要求实例化将是不必要和令人困惑的。 。请注意，它是最终的，并且其所有成员都是静态的。如果Java允许将顶级类声明为static，那么Math类确实是静态的。

What good are static classes? A good use of a static class is in defining one-off, utility and/or library classes where instantiation would not make sense. A great example is the Math class that contains some mathematical constants such as PI and E and simply provides mathematical calculations. Requiring instantiation in such a case would be unnecessary and confusing. See Java's Math class. Notice that it is final and all of its members are static. If Java allowed top-level classes to be declared static then the Math class would indeed be static.

这篇关于Java中的静态类的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！