读书笔记:《Effective Java中文版第二版》

1.创建和销毁对象

• 第一条：考虑用静态工厂方法替代构造器

public static Boolean valueOf(boolean b){
  return b ? Boolean.TRUE : Boolean.FALSE;
}

• 第二条：遇到多个构造器参数时要考虑用构建器

//重叠构造器模式
public class Demo {
  private final int a;
  private final int b;
  private final int c;
  public Demo(int a){
    this(a,0);
  }
  public Demo(int a,int b){
    this(a,b,0);
  }
  public Demo(int a,int b,int c){
    this.a = a;
    this.b = b;
    this.c = c;
  }
}

//JavaBean模式
public class Demo {
    private int a = -1;
    private int b = 0;
    private int c = 0;
    public Demo() {
    }
    public void setA(int a) {
        this.a = a;
    }
    public void setB(int b) {
        this.b = b;
    }
    public void setC(int c) {
        this.c = c;
    }
}

//Builder模式
public class Demo {
    private final int a;
    private final int b;
    private final int c;
    public static class Builder{
        private final int a;
        private int b = 0;
        private int c = 0;
        public Builder(int a){
            this.a = a;
        }
        public Builder b(int val){
            b = val;
            return this;
        }
        public Builder c(int val){
            c = val;
            return this;
        }
        public Demo build(){
            return new Demo(this);
        }
    }
    private Demo(Builder builder){
        a = builder.a;
        b = builder.b;
        c = builder.c;
    }
}

这里a是必填参数无默认值，b是非必填参数有默认值

    public static void main(String[] args) {
        Demo demo1 = new Builder(250).b(12).c(36).build();
        Demo demo2 = new Builder(250).c(36).build();
    }