javascript如何在java中操作类

1 周，4 日 Questions & Answers 186

我懂sereval编程语言。其中大多数是脚本语言，如lua、perl、JS、ruby等

但最近，我开始用Java编程，它安静地工作。所以我一直在考虑JS中存在的某个函数。构造函数的原型，即。为了进一步了解我的问题到底是什么，我将用JS做一个例子。假设您想创建一个狗的应用程序

function dog (){
this.property1 = value;
this.propertr2 = value2;
this.propertyN = valueN;
//et.c.
}

//now, I will create sereval instances of the constructor in JS

var snoopy = new dog();
var buddy = new dog();

我所知道的关于JS的一点是，你可以动态地改变构造函数和该构造函数的所有实例的信息（在JS中称为prototype）的关键字如下：

dog.prototype.bark = function () {
console.log("Woof!");
};

这不仅改变了关于构造器的信息，使每个用构造器创造的狗都知道如何吠叫，而且也改变了构造器的所有实例都得到了原型插入的信息，在这种情况下，它教狗如何吠叫。我们可以在下一个示例中看到：

var someOtherDog = new dog ();
someOtherDog.bark(); //output will be: Woof!
snoopy.bark();       //output will also be: Woof!
buddy.bark();        //you guest it! it will also be: Woof!

So with this prototype keyword in JS I can manipulate constructors and their instances. Now, my question is:

如何在java中操作类及其实例？这可能吗？若有,；为了在java中实现类似的功能，我应该做什么

class dog
{
    private String hairColor;
    public dog ()
    {
        hairColor = "Brown";
    }
    public static void main (String args[])
    {
        dog snoopy = new dog ();
        dog buddy = new dog ();
        //now, how do I manipulate the class like I did in JS?
    }
}

# 3 楼答案

如果需要，可以动态创建匿名类

假设你有一门课：

class Dog {
    String name;
    Dog(String name) { this.name = name; }
    void bark() { System.out.println(name + " says 'woof!'"); }

    public static void main(String...args) { 
        Dog snoopy = new Dog("snoopy");
        snoopy.bark();
    }

}

这是结果

c:\files\j>javac Dog.java

c:\files\j>java Dog
snoopy says 'woof!'

现在，伙计，他不是说汪汪，而是说拉夫！所以我们像这样在飞行中创造了一个

class Dog {
    String name;
    Dog(String name) { this.name = name; }
    void bark() { System.out.println(name + " says 'woof!'"); }

    public static void main(String...args) { 
        Dog snoopy = new Dog("snoopy");
        snoopy.bark();
        Dog buddy = new Dog("buddy") {
            @Override void bark() { System.out.println(name + " says 'ruff!'"); }
        };
        buddy.bark();
    }

}

导致

c:\files\j>javac Dog.java

c:\files\j>java Dog
snoopy says 'woof!'
buddy says 'ruff!'

如果你想永久性地改变每只狗，这会变得更加困难，但可以通过策略模式来实现

假设我们有以下几点

abstract class BarkingStrategy {
    public abstract void doBark(Dog dog);
}

class TypicalBarkingStrategy extends BarkingStrategy {
    public void doBark(Dog dog) { System.out.println(dog.getName() + " says 'woof!'"); }
}

class AggressiveBarkingStrategy extends BarkingStrategy {
    public void doBark(Dog dog) { System.out.println(dog.getName() + " says 'Rrrruff!'"); }
}

class Dog {
    // notice this is static - that means it belongs to the class itself, not 
    // any particular instance of it - similar to prototype
    static BarkingStrategy bark = new TypicalBarkingStrategy();
    String name;
    Dog(String name) { this.name = name; }
    String getName() { return name; }
    void bark() { bark.doBark(this); }
}

然后您可以执行以下操作

public static void main(String...args) {
    Dog snoopy = new Dog("snoopy");
    snoopy.bark();
    Dog.bark = new AggressiveBarkingStrategy();
    snoopy.bark();
}

这导致

c:\files\j>javac Dog.java

c:\files\j>java Dog
snoopy says 'woof!'
snoopy says 'Rrrruff!'

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javascript如何在java中操作类

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