链式方法设计

Question

我写了一个简单的类来演示链样式方法设计:

public class Cal {

    private Cal(){}

    private boolean isCheckArguments = false;

    public static Cal useAbs() {
        return new Cal(){   
          @Override int check(int i) {
                return Math.abs(i);
            }};
    }

    public static Cal useNormal() {
        return new Cal();
    }   

    public Cal checkArguments() {
        isCheckArguments =true;
        return this;
    }

     int check(int i){ return i;}

     public int plus(int i, int j) {    
        if(isCheckArguments && i<j){
            throw new IllegalArgumentException("i<j!");
        }
        return check(i+j);
    }
}

所以客户端代码可以是:

Cal cal = Cal.useAbs().checkArguments();
int sum = cal.plus(100,2);//IllegalArgumentException occurs

Cal cal2 = Cal.useAbs();
int sum2 = cal.plus(-100,2);//98

Cal cal3 = Cal.useNormal();
int sum3 = cal.plus(-100,2);//-98

我的问题是:这是一个合理的设计吗？比较:int plus(int a, int b, boolean useAbs, boolean checkArguments).谢谢!

Answer 1

听起来你想要一个流畅的界面来构建服务类.番石榴也做类似的事情.你会做这样的事情:

public interface Cal {
   int plus(int a, int b);
}

public class CalBuilder {
    class InternalCal implements Cal {
       boolean useAbs;
       boolean checkArgs;
       public int plus(int a, int b) {
          if(checkArgs) {
             // blah, blah blah
          }
          if(useAbs) {
             // doodle bug, doodle darn
          }
          return a+b; // whatevs
       }
    }
    boolean absSet=false;
    InternalCal holder=new InternalCal();
    public CalBuilder useNormal() {
        if(absSet) { throw new IllegalArgumentException(); } // already called
        holder.useAbs=false;    
        absSet=true;
        return this;
    }

    public CalBuilder useAbs() {
        if(absSet) { throw new IllegalArgumentException(); } // already called
        holder.useAbs=false;    
        absSet=true;
        return this;
    }

    public CalBuilder checkArguments() {
       if(holder.checkArgs) { throw new IllegalArgumentException(); }
       holder.checkArgs=true;
       return this;
    }

    public Cal build() {
       return holder;
    }
}

用法如下所示:

Cal cal=new CalBuilder().useAbs().checkArguments().build();
int sum=cal.plus(1,2);