Nesting builder pattern classes in Java

Question

I am trying to create a java class for a line graph (using builder pattern) that encloses many properties within. Based on the application of these properties, I am trying to create inner builder classes (such as X-Axis Properties, Y-Axis properties etc). I am new to Java and I would like to know if it is possible to invoke builder objects like below in my example. I followed through a link Can the builder pattern ever be doing too much?. that would build objects in increments. I liked the idea. However, I do not know how could I put it to use for my scenario.

Invoke method:

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

Is it possible to call .build() statement only once to create all objects instead of repeating it multiple times?

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);}
}

In your question "to call .build() statement only once to create all objects " . Were you meant to write "to call .build() statement only once to create the with all the properties set " — Sajeev
– Sajeev, Commented Apr 19, 2016 at 1:16

Radiodef · Accepted Answer · 2016-04-19 02:05:58Z

One way you could do it would be like this, where you have 3 builder objects that can all reference each other and switch between them. It's similar to what you were already trying to do:

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(); }
    }
}

A more complicated example is to write something similar to the way a step builder works. We define interfaces for each of the "steps" and implement all of them in a single class. Each of the methods that "switches" the properties actually returns 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();
}

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