更新时间:2021-12-29 08:22:20
让Builder构造函数以旧对象为参数,并设置任何你想从它到新的。
Make the Builder constructor take as an argument the "old" object and set whatever you want from it to the new one.
编辑
您需要阅读更多关于构建器模式的信息更好地掌握它是什么,如果你真的需要它。
You need to read a bit more about the builder pattern to get a better grasp at what it is and if you really need it.
一般的想法是,当你有可选元素。有效的Java项目2是您***的朋友。
The general idea is that Builder pattern is used when you have optional elements. Effective Java Item 2 is your best friend here.
对于您的类,如果要从另一个构建一个对象并同时使用Builder模式, / p>
For your class, if you want to build one object from another and use a Builder pattern at the same time, you
那么这样看起来如何?我将只提供第一个你可以自己找出第二个。
So how does that looks like? I am going to provide only the first one you can figure out the second on your own.
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;
}
}
您将如何从另一个创建一个对象: / p>
And how you will create one object from another:
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