使用子类中构造函数的Builder模式 [英] use Builder pattern from the constructor in a subclass
问题描述
我目前正在使用Builder模式,紧跟维基百科文章中提出的Java实现 Builder模式 http://en.wikipedia.org/wiki/Builder_pattern
I am currently using the Builder pattern, following closely the Java implementation suggested in the Wikipedia article Builder pattern http://en.wikipedia.org/wiki/Builder_pattern
这是一个示例代码,用于说明我的实现
This is a sample code that ilustrates my implementation
public class MyPrimitiveObject {
private String identifier="unknown";
public static class Builder {
private final MyPrimitiveObject obj = new MyPrimitiveObject();
public MyPrimitiveObject build() { return obj; }
public Builder setidentifier (String val) {
obj.identifier = val;
return this;
}
}
public static Builder createBuilder() { return new Builder(); }
@Override public String toString() { return "ID: "+identifier; }
}
在我的一些使用这个类的应用程序中,我碰巧找到了类似的构建代码,所以我想在 MySophisticatedObject
中继承 MyPrimitiveObject
,并将所有重复的代码移动到其构造函数中。这是问题所在。
In some of my applications that use this class, I happen to find very similar building code , so I thought to subclass MyPrimitiveObject
in MySophisticatedObject
and move all my repeated code into its constructor.. and here is the problem.
我如何调用超类构建器并将其返回的对象指定为我的实例?
How may I invoke the superclass Builder and assign its returned object as my instance?
public class MySophisticatedObject extends MyPrimitiveObject {
private String description;
public MySophisticatedObject (String someDescription) {
// this should be the returned object from build() !!
Builder().setidentifier(generateUUID()).build()
description = someDescription;
}
}
推荐答案
你可能要考虑具有嵌套的 MySophisticatedObject.Builder
延伸 MyPrimitiveObject.Builder
,并覆盖其 build()
方法。在构建器中有一个受保护的构造函数,以接受要设置值的实例:
You might want to consider having a nested MySophisticatedObject.Builder
which extends MyPrimitiveObject.Builder
, and overrides its build()
method. Have a protected constructor in the builder to accept the instance on which to set values:
public class MyPrimitiveObject {
private String identifier="unknown";
public static class Builder {
private final MyPrimitiveObject obj;
public MyPrimitiveObject build() { return obj; }
public Builder setidentifier (String val) {
obj.identifier = val;
return this;
}
public Builder() {
this(new MyPrimitiveObject());
}
public Builder(MyPrimitiveObject obj) {
this.obj = obj;
}
}
...
}
public class MySophisticatedObject extends MyPrimitiveObject {
private String description;
public static class Builder extends MyPrimitiveObject.Builder {
private final MySophisticatedObject obj;
public Builder() {
this(new MySophisticatedObject());
super.setIdentifier(generateUUID());
}
public Builder(MySophisticatedObject obj) {
super(obj);
this.obj = obj;
}
public MySophisticatedObject build() {
return obj;
}
// Add code to set the description etc.
}
}
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