Java：获取类的属性来构造字符串表示 [英] Java: Getting the properties of a class to construct a string representation

问题描述

假设我有一个这样的类（并且还假设所有的私有变量：

  public class Item { 
 private String _id = null; 
 private String _name = null; 
 private String _description = null; 
 
 ... 
} 
  

现在，如果我想构建一个toString class：

  @Override 
 public String toString（）{
 return（_id ++ _name ++ _description）; 
} 
  

但是如果我说15个私有变量在类中？我必须写这样的每个变量的名称吗？

理想情况下，我想通过迭代列表来完成任务的私有变量并构造字符串表示形式：

  @Override 
 public String toString（）{
 ArrayList< String> members = getClass（）。getMembers（）; //像这样的一些方法
 String string =; 
 for（...）
 string + = members [i] +; 
} 
  

或者一个toJSON方法，我仍然需要访问这些变量。任何建议？

解决方案

您可以：

  @Override 
 public String toString（）{
 StringBuilder sb = new StringBuilder（）; 
 sb.append（getClass（）。getName（））; 
 sb.append（：）; 
 for（Field f：getClass（）。getDeclaredFields（））{
 sb.append（f.getName（））; 
 sb.append（=）; 
 sb.append（f.get（this））; 
 sb.append（，）; 
} 
 return sb.toString（）; 
} 
  

不要使用字符串连接构造最终结果来自15个数据成员，特别是如果 toString（）将被调用很多。内存碎片和开销可能真的很高。使用 StringBuilder 构建大型动态字符串。

我通常得到我的IDE（IntelliJ） $ c> toString（）方法，而不是使用反射为此。

另一个有趣的方法是使用来自Project Lombok的@ ToString注释：

  import lombok.ToString; 
 
 @ToString（excludes =id）
 public class ToStringExample {
 private static final int STATIC_VAR = 10; 
 private String name; 
 private形状shape = new Square（5，10）; 
 private String [] tags; 
 private int id; 
 
 @ToString（callSuper = true，includeFieldNames = true）
 public static class Square extends {
 private final int width，height; 
 
 public Square（int width，int height）{
 this.width = width; 
 this.height = height; 
} 
} 
} 
  

我发现这更好一些，比如说，Jakarta Commons toString构建器，因为这种方法是更可配置的，它也是在编译时构建而不是运行时。

Let's say I have a class like this (and also further assume that all the private variables:

public class Item {
    private String _id = null;
    private String _name = null;
    private String _description = null;

        ...
}

Now, if I want to build a toString() representation of this class, I would do something like this inside the Item class:

@Override
public String toString() {
    return (_id + " " + _name + " " + _description);
}

But what if I have say 15 private variables inside the class? Do I have to write the name of each and every variable like this?

Ideally, I would like to get over with the task by iterating through the list of private variables of this class and construct the string representation:

@Override
public String toString() {
    ArrayList<String> members = getClass().getMembers(); //Some method like this
    String string = "";
    for(...)
        string += members[i] + " ";
}

Or perhaps a toJSON method, I would still need access to the names of these variables. Any suggestions?

解决方案

You could do:

@Override
public String toString() {
  StringBuilder sb = new StringBuilder();
  sb.append(getClass().getName());
  sb.append(": ");
  for (Field f : getClass().getDeclaredFields()) {
    sb.append(f.getName());
    sb.append("=");
    sb.append(f.get(this));
    sb.append(", ");
  }
  return sb.toString();
}

Don't use string concatenation to construct an end result from 15 data members, particularly if the toString() will be called a lot. The memory fragmentation and overhead could be really high. Use StringBuilder for constructing large dynamic strings.

I usually get my IDE (IntelliJ) to simply generate toString() methods for me rather than using reflection for this.

Another interesting approach is to use the @ToString annotation from Project Lombok:

import lombok.ToString;

@ToString(excludes="id")
public class ToStringExample {
  private static final int STATIC_VAR = 10;
  private String name;
  private Shape shape = new Square(5, 10);
  private String[] tags;
  private int id;

  @ToString(callSuper=true, includeFieldNames=true)
  public static class Square extends Shape {
    private final int width, height;

    public Square(int width, int height) {
      this.width = width;
      this.height = height;
    }
  }
}

I find this much more preferable to, say, Jakarta Commons toString builders because this approach is far more configurable and it's also built at compile-time not run-time.

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