My Preferred Builder Style - subtle and sweet. Unit testing friendly.

PreferredBuilder.java

public class PreferredBuilder {
  private String a;
  private int i;
  
    public PreferredBuilder() {
      
    }
    
    public PreferredBuilder(Builder builder) {
      this.a = builder.a;
      this.i = builder.i;
    }
  
    public String getA() {
        return a;
    }

    public void setA(final String a) {
        this.a = a;
    }
    
    public int getI() {
        return i;
    }

    public void setI(final int i) {
        this.i = i;
    }
    
    public static class Builder<T extends Builder> {
      private String a;
      private int i;
      
      public Builder clear () {
        a = null;
        i = 0;
        return this;
      }
      
      public Builder a(final String a) {
        this.a = a;
        return this;
      }
      
      public Builder i(final int i) {
        this.i = i;
        return this;
      }
      
      public BilledUsage build() {
          return new BilledUsage(this);
      }
    }
    
}