java - Java 中的嵌套构建器模式类

Question

我正在尝试为线图创建一个java类(使用构建器模式)，其中包含许多属性。基于这些属性的应用，我尝试创建内部构建器类(例如 X 轴属性、Y 轴属性等)。我是 Java 新手，我想知道是否可以像下面的示例一样调用构建器对象。我点击了链接Can the builder pattern ever be doing too much? 。它将以增量方式构建对象。我喜欢这个主意。但是，我不知道如何将其用于我的场景。

调用方法:

new LineGraph().UiPropBuilder(ctx)
               .setBackgroundColor(Color.BLUE)
               .build()
               .XAxisProperties()
               .enableGridLines(true)
               .build()
               .YAxisProperties()
               .enableGridLines(false)
               .build();

是否可以仅调用 .build() 语句一次来创建所有对象，而不是重复多次？

类(class):

public class LineGraph{

   private LineGraph()

   public static class UiPropBuilder{

      private Integer mBackgroundColor;
      private Boolean bTouchEnabled;
      ...

      public UiPropBuilder (Context ctx) { this.ctx = ctx; }

      public UiPropBuilder setBackgroundColor(Integer mBackgroundColor){ this.mBackgroundColor = mBackgroundColor; return this;}

      public UiPropBuilder touchEnabled(Boolean bTouchEnabled){ this.bTouchEnabled = bTouchEnabled; return this;}

      ... some more properties...
      public UiPropBuilder build(){ return new UiPropBuilder(this); }     

   }

// X-Axis properties builder
public static class XAxisProperties{
   // variable declarations and constructor omitted
   public XAxisProperties enableGridLines(Boolean enable) {this.enable = enable); return this;}
   public XAxisProperties build(){ return new XAxisProperties(this);}


// Y-Axis properties Builder

public static class YAxisProperties{
   // variable declarations and constructor omitted
   public YAxisProperties enableGridLines(Boolean enable) {this.enable = enable); return this;}
   public YAxisProperties build(){ return new YAxisProperties(this);}
}

Answer 1

一种方法是这样，您有 3 个构建器对象，它们都可以互相引用并在它们之间切换。这与您已经尝试做的事情类似:

public static class UiPropBuilder {
    private XAxisProperties xAxisProperties = new XAxisProperties();
    private YAxisProperties yAxisProperties = new YAxisProperties();
    // ...
    public XAxisProperties xAxisProperties() { return xAxisProperties; }
    public YAxisProperties yAxisProperties() { return yAxisProperties; }

    public LineGraph build() {
        return new LineGraph(..., ..., ..., ...);
    }

    public class XAxisProperties {
        // ...
        public YAxisProperties yAxisProperties() { yAxisProperties; }
        public UiPropBuilder uiProperties() { return UiPropBuilder.this; }
        public LineGraph build() { return UiPropBuilder.this.build(); }
    }

    public class YAxisProperties {
        // ...
        public XAxisProperties xAxisProperties() { return xAxisProperties; }
        public UiPropBuilder uiProperties() { return UiPropBuilder.this; }
        public LineGraph build() { return UiPropBuilder.this.build(); }
    }
}

一个更复杂的示例是编写类似于步骤构建器工作方式的代码。我们为每个“步骤”定义接口(interface)，并在单个类中实现所有这些接口(interface)。每个“切换”属性的方法实际上都会返回 this。

public interface BuildStep       { LineGraph        build();           }
public interface UiSwitchStep    { UiPropBuilder    uiProperties();    }
public interface XAxisSwitchStep { XAxisPropBuilder xAxisProperties(); }
public interface YAxisSwitchStep { YAxisPropBuilder yAxisProperties(); }

public interface UiPropBuilder
extends XAxisSwitchStep, YAxisSwitchStep, BuildStep {
    // UI property setters
    // ...
}

public interface XAxisPropBuilder
extends YAxisSwitchStep, UiSwitchStep, BuildStep {
    // X-axis property setters
    // ...
}

public interface YAxisPropBuilder
extends XAxisSwitchStep, UiSwitchStep, BuildStep {
    // Y-axis property setters
    // ...
}

private static class UiBuilderImpl
implements UiPropBuilder, XAxisPropBuilder, YAxisPropBuilder {
    // implement ALL property setters
    // ...

    @Override
    public XAxisProperties xAxisProperties() {
        return this;
    }
    @Override
    public YAxisProperties yAxisProperties() {
        return this;
    }
    @Override
    public UiPropBuilder uiProperties() {
        return this;
    }
    @Override
    public LineGraph build() {
        return new LineGraph(..., ..., ..., ...);
    }
}

// create new builders through a static method
// which returns the interface type
public static UiPropBuilder builder() {
    return new UiBuilderImpl();
}