Java - 应该通过getters和setters方法在构造函数中访问私有实例变量吗？ [英] Java - Should private instance variables be accessed in constructors through getters and setters method?

问题描述

但是当我在IDE的帮助下生成构造函数时，它直接初始化实例变量而不是通过他们的setter方法初始化它们。

Q1。因此，我应该更改IDE生成的构造函数代码，以通过它们的setter方法初始化这些实例变量。

Q2。如果是的话，为什么IDE不以这种方式生成构造函数代码？

===================== ========== EDITED ===================================

• 我使用Eclipse和Netbeans IDE。




• 一个一般问题。但是根据@Lords的要求，答案取决于我们的构造函数是public还是protected，还是私有还是私有？

解决方案

您应该从不从构造函数调用非最终方法。类构造函数用于初始化对象，并且对象在构造函数返回之前不处于一致状态。如果你的构造函数调用了一个非最终的方法，后来被一个子类覆盖，你可能会得到奇怪的，意想不到的结果，因为对象在调用重写的方法时没有完全初始化。

考虑这个假设的例子：

  class A {
 private int x; 
 
 public A（）{
 setX（2）; 
} 
 
 public void setX（int x）{
 this.x = x; 
} 
 
 public int getX（）{
 return x; 
} 
} 
 
 B类扩展A {
 private int number = 10; 
 
 @Override 
 public void setX（int x）{
 //将x设置为数字的值：10 
 super.setX（number）; 
} 
} 
 
 public class Test {
 public static void main（String [] args）{
 B b = new B（）; 
 // b.getX（）应该是10，对不对？ 
 System.out.println（B.getX（）=+ b.getX（））; 
} 
} 
  

此程序的输出为：

  B.getX（）= 0 
  

原因是 B 的号成员在此时未初始化 setX ，因此使用其默认值 0 。

本文有更全面的解释，有效的Java 。

I know that private instance variables are accessed through their public getters and setters method.

But when I generate constructors with the help of IDE, it initializes instance variables directly instead of initializing them through their setter methods.

Q1. So should I change the IDE generated code for constructors to initialize those instance variables through their setter methods.

Q2. If yes, then why IDE don't generate constructors code in that way?

============================= EDITED =======================================

• I use Eclipse and Netbeans IDE

• It's a general question. But as asked by @Lords would the answer depends on whether our constructor is public or protected or package private or private?

解决方案

You should never call a non-final method from a constructor. A class constructor is used to initialize an object, and the object is not in a consistent state until the constructor returns. If your constructor calls a non-final method which is later overridden by a subclass, you can get strange, unexpected results because the object is not fully initialized when the overridden method is called.

Consider this contrived example:

class A {
    private int x;

    public A() {
        setX(2);
    }

    public void setX(int x) {
        this.x = x;
    }

    public int getX() {
        return x;
    }
}

class B extends A {
    private int number = 10;

    @Override        
    public void setX(int x) {
        // set x to the value of number: 10
        super.setX(number);
    }
}

public class Test {
    public static void main(String[] args) {
        B b = new B();
        // b.getX() should be 10, right?
        System.out.println("B.getX() = " + b.getX());
    }
}

The output of this program is:

B.getX() = 0

The reason is that B's number member is not initialized at the time setX is called, so its default value of 0 is used.

This article has a more thorough explanation, as does Effective Java.

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