创建与“旧”的对象引用Builder模式新对象

Question

我用Builder模式玩耍和被卡住了如何在新的“属性”添加到新创建的对象：

public class MsProjectTaskData { 
    private boolean isAlreadyTransfered; 
    private String req;  

    public static class Builder {  
    private boolean isAlreadyTransfered = false; 

    public Builder withTransfered(boolean val) { 
     isAlreadyTransfered = val; 
     return this; 
    }  
    public MsProjectTaskData build() { 
     return new MsProjectTaskData(this); 
    } 
    } 

    private MsProjectTaskData(Builder builder) { 
    isAlreadyTransfered = builder.isAlreadyTransfered; 
    } 

    public MsProjectTaskData(String req) { 
    this.req = req; 
    } 
} 

我可以创建生成一个新的对象是这样的：

MsProjectTaskData data = new MsProjectTaskData.Builder().withTransfered(true).build(); 

但这种方法从一个新创建的对象的字符串req丢失（当然）。

是否有可能用新的集合isAlreadyTransfered变量创建一个新对象，与来自“旧”对象的“旧”req字符串？

也许我必须将旧的对象引用传递给Builder，但我不知道该怎么做。也许使用Builder模式对于这种方法并不真正有用？

编辑：

思（尤金评论）之后，我知道了：

public static class Builder { 
private boolean isAlreadyTransfered = false; 
private MsProjectTaskData data; 

public Builder(MsProjectTaskData data) { 
    this.data = data; 
} 

public Builder withTransfered(boolean val) { 
    isAlreadyTransfered = val; 
    data.setAlreadyTransfered(isAlreadyTransfered); 
    return this; 
} 
public MsProjectTaskData build() { 
    return data; 
} 
} 

似乎工作或者是什么问题上面的代码？我可以不加考虑地使用这种方法吗？

Answer 1

使Builder构造函数将“old”对象作为参数并将其设置为新的对象。

编辑

你需要阅读更多的关于建造者模式它是什么，以获得更好的把握，如果你真的需要它。

总的想法是，当你有可选元素时使用Builder模式。有效的Java项目2是您最好的朋友。

对于你的类，如果你想从另一个构建一个对象，并在同一时间使用Builder模式，你

1. 要么通过“旧”对象在Builder构造
2. 创建方法从或源自古等

那么，如何看起来像？我将只提供第一个，你可以自己找出第二个。

class MsProjectTaskData { 
    private final String firstname; 
    private final String lastname; 
    private final int age; 

    private MsProjectTaskData(Builder builder){ 
     this.firstname = builder.firstname; 
     this.lastname = builder.lastname; 
     this.age  = builder.age; 
    } 

    public static final class Builder{ 
     //fields that are REQUIRED must be private final 
     private final String firstname; 
     private final String lastname; 

     //fields that are optional are not final 
     private int age; 

     public Builder(String firstname, String lastname){ 
      this.firstname = firstname; 
      this.lastname = lastname; 
     } 

     public Builder(MsProjectTaskData data){ 
      this.firstname = data.firstname; 
      this.lastname = data.lastname; 
     } 

     public Builder age(int val){ 
      this.age = val; return this; 
     } 

     public MsProjectTaskData build(){ 
      return new MsProjectTaskData(this); 
     } 
    } 

    public String getFirstname() { 
     return firstname; 
    } 

    public String getLastname() { 
     return lastname; 
    } 

    public int getAge() { 
     return age; 
    } 
} 

你会如何生成另一个对象：

MsProjectTaskData.Builder builder = new MsProjectTaskData.Builder("Bob", "Smith"); 
    MsProjectTaskData oldObj = builder.age(23).build(); 
    MsProjectTaskData.Builder newBuilder = new MsProjectTaskData.Builder(oldObj); 
    MsProjectTaskData newObj = newBuilder.age(57).build(); 
    System.out.println(newObj.getFirstname() + " " + newObj.getLastname() + " " + newObj.getAge()); // Bob Smith 57 

Answer 2

我将其更改为

public class MsProjectTaskData { 
    private boolean transfered; 
    private String request;  

    public static class Builder {  
     private boolean transfered = false; 
     private String request; 

     public Builder() { 
      // empty 
     } 

     public Builder(MsProjectTaskData old) { 
      this.request(old.request); 
      this.transfered(old.transfered); 
     } 

     public Builder request(String val) { 
      request = val; 
      return this; 
     } 

     public Builder transfered(boolean val) { 
      transfered = val; 
      return this; 
     }  
     public MsProjectTaskData build() { 
      return new MsProjectTaskData(this); 
     } 
    } 

    private MsProjectTaskData(Builder builder) { 
     transfered = builder.transfered; 
     request = builder.request; 
    } 

} 

而且这样

MsProjectTaskData data = new MsProjectTaskData.Builder().transfered(true).request("request").build(); 
MsProjectTaskData changedData = new MsProjectTaskData.Builder(data).transfered(false).request("changeRequest").build(); 
MsProjectTaskData sameData = new MsProjectTaskData.Builder(data).build(); 

使用我拿了自由将布尔变成“转移”，我觉得这很容易理解