Effective Java第二条：遇到多个构造器参数时要考虑用构建器

1， 对于一个类具有很多可选参数时，我们考虑使用：a，重叠构造器（telescoping constructor），b，JavaBean模式。C，构建器即Builder模式

2， 重叠构造器模式下，第一个只有必要参数的构造器，第二个构造器有一个可选参数，第三个构造器有两个，以此类推。

3， Javabean模式提供了set方法来设置值。但是其有可能出于不一致状态，所以我们必须保证其线程安全。

4， 构建起模式（builder）

public  class  Builderpattern{
			private final int a;
			private final int b;
			private final int c;
			private final int d;
			private final int e;
			private final int f;
		 	public static class Builder{
				private final int a;
				private final int b;
			
				private final int c=0;
				private final int d=0;
				private final int e=0;
				private final int f=0;
	 	 		public Builder(int a,int b){
					this.a=a;
					this.b=b;		
				}
				public Builder c(int val)
				{c=val; return this;}
				public Builder d(int val)
				{d=val;return this;}
				public Builder e(int val)
				{e=val;return this;}
				public Builder f(int val)
				{f=val;return this;}
				
				public Builderpattern build(){
					return new Builderpattern(this);
				}
			}
			
			Private Builderpattern(Builder builder){
				a=builder.a;
				b=builder.b;
				c=builder.c;
				d=builder.d;
				e=builder.e;
				f=builder.f;

			}
}

客户端代码
Builderpattern cc=new Builderpattern.Builder(240,8).c(100).d(35).e(45).builder();

评论

1 楼 小小黑咖啡 2011-03-18  

这位朋友你好，很高兴你能写这篇帖子，但是代码的错误有点多，下次希望你能在eclipse打出来之后再贴上去。这是我改的代码，你看下对吗。相互学习

public  class  Builderpattern{
			private final int a;
			private final int b;
			private final int c;
			private final int d;
			private final int e;
			private final int f;
		 	public static class Builder{
				private final int a;
				private final int b;
			
				private int c=0;
				private int d=0;
				private int e=0;
				private int f=0;
	 	 		public Builder(int a,int b){
					this.a=a;
					this.b=b;		
				}
				public Builder c(int val)
				{c=val; return this;}
				public Builder d(int val)
				{d=val;return this;}
				public Builder e(int val)
				{e=val;return this;}
				public Builder f(int val)
				{f=val;return this;}
				
				public Builderpattern build(){
					return new Builderpattern(this);
				}
			}
			
			private Builderpattern(Builder builder){
				a=builder.a;
				b=builder.b;
				c=builder.c;
				d=builder.d;
				e=builder.e;
				f=builder.f;

			}
}

客户端代码

Builderpattern cc=new Builderpattern.Builder(240,8).c(100).d(35).e(45).build();