創建與「舊」的對象引用Builder模式新對象

Question

我用Builder模式玩耍和被卡住瞭如何在新的「屬性」添加到新創建的對象：

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; 
    } 
} 

我可以創建生成一個新的對象是這樣的：

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

但這種方法從一個新創建的對象的字符串req丟失（當然）。

是否有可能用新的集合isAlreadyTransfered變量創建一個新對象，與來自「舊」對象的「舊」req字符串？

也許我必須將舊的對象引用傳遞給Builder，但我不知道該怎麼做。也許使用Builder模式對於這種方法並不真正有用？

編輯：

思（尤金評論）之後，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; 
} 
} 

似乎工作或者是什麼問題上面的代碼？我可以不加考慮地使用這種方法嗎？

Answer 1

使Builder構造函數將「old」對象作爲參數並將其設置爲新的對象。

編輯

你需要閱讀更多的關於建造者模式它是什麼，以獲得更好的把握，如果你真的需要它。

總的想法是，當你有可選元素時使用Builder模式。有效的Java項目2是您最好的朋友。

對於你的類，如果你想從另一個構建一個對象，並在同一時間使用Builder模式，你

1. 要麼通過「舊」對象在Builder構造
2. 創建方法從或源自古等

那麼，如何看起來像？我將只提供第一個，你可以自己找出第二個。

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; 
    } 
} 

你會如何生成另一個對象：

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

我將其更改爲

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; 
    } 

} 

而且這樣

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(); 

使用我拿了自由將布爾變成「轉移」，我覺得這很容易理解