java中使用Builder模式构建多个参数的构造器

public class BeanEntity{    private int variable1;//必选参数    private int variable2;//必选参数    private int variable3;//可选参数    private int variable4;//可选参数    private BeanEntity(Builder builder){        this.variable1 = builder.variable1;        this.variable2 = builder.variable2;        this.variable3 = builder.variable3;        this.variable4 = builder.variable4;    }    public static class Builder{        private int variable1;        private int variable2;        private int variable3;        private int variable4;        public Builder(int variable1, int variable2){            this.variable1 = variable1;            this.variable2 = variable2;        }        public Builder setVariable3(int variable3){            this.variable3= variable3;            return this;        }        public Builder setVariable4(int variable4){            this.variable4= variable4;            return this;        }        public BeanEntity build(){            return new BeanEntity(this);        }    }}

使用

 BeanEntity entity = new BeanEntity.Builder(100, 200)             .setVariable3(300)             .setVariable4(400)             .build();