Java：向现有Class添加字段和方法？ [英] Java: Adding fields and methods to existing Class?

问题描述

在Java中，是否有一种向现有类添加某些字段和方法的方法？
我想要的是我有一个类导入到我的代码中，我需要添加一些从现有字段派生的字段及其返回方法。
有没有办法做到这一点？

Is there, in Java, a way to add some fields and methods to an existing class? What I want is that I have a class imported to my code, and I need to add some fields, derived from the existing fields, and their returning methods. Is there any way to do this?

推荐答案

您可以用Java扩展类。例如：

You can extend classes in Java. For Example:

public class A {

  private String name;

  public A(String name){
    this.name = name;
  }

  public String getName(){
    return this.name;
  }

  public void setName(String name) {
    this.name = name;
  }

}

public class B extends A {
  private String title;

  public B(String name, String title){
    super(name); //calls the constructor in the parent class to initialize the name
    this.title= title;
  }      

  public String getTitle(){
    return this.title;
  }

  public void setTitle(String title) {
    this.title= title;
  }
}

现在 B 可以访问 A 中的公共字段：

Now instances of B can access the public fields in A:

B b = new B("Test");
String name = b.getName();
String title = b.getTitle();

有关更详细的教程，请查看继承（Java教程>学习Java语言>接口和继承）。

For more detailed tutorial take a look at Inheritance (The Java Tutorials > Learning the Java Language > Interfaces and Inheritance).

编辑：如果类 A 有一个构造函数，如：

If class A has a constructor like:

public A (String name, String name2){
  this.name = name;
  this.name2 = name2;
}

然后在班级 B 你有：

public B(String name, String name2, String title){
  super(name, name2); //calls the constructor in the A 
  this.title= title;
}

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