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Compare different object types with comparator

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有刺的猬
有刺的猬 2021-01-06 06:10

I need to write a Comparator that take an object A of type A and an object B of type B. The two object are not an extention of a common object. They are really diffferent, b

2条回答
  • 醉梦人生
    醉梦人生 (楼主)
    2021-01-06 07:00

    There's a very hacky way of doing it that allows you to use Object and instanceof but if you can implement a proxy class that exposes a specific interface you would be better off doing that.

    class A {

    public String getSomething() {
        return "A";
    }
}

class B {

    public String getSomethingElse() {
        return "B";
    }
}

class C implements Comparator {

    @Override
    public int compare(Object o1, Object o2) {
        // Which is of what type?
        A a1 = o1 instanceof A ? (A) o1: null;
        A a2 = o2 instanceof A ? (A) o2: null;
        B b1 = o1 instanceof B ? (B) o1: null;
        B b2 = o2 instanceof B ? (B) o2: null;
        // Pull out their values.
        String s1 = a1 != null ? a1.getSomething(): b1 != null ? b1.getSomethingElse(): null;
        String s2 = a2 != null ? a2.getSomething(): b2 != null ? b2.getSomethingElse(): null;
        // Compare them.
        return s1 != null ? s1.compareTo(s2): 0;
    }

}



    The more acceptable mechanism would be to implement a proxy class for each that implements a common interface tyhat can then be compared using a proper type-safe comparator.
    


    interface P {

    public String getValue();
}

class PA implements P {

    private final A a;

    PA(A a) {
        this.a = a;
    }

    @Override
    public String getValue() {
        return a.getSomething();
    }
}

class PB implements P {

    private final B b;

    PB(B b) {
        this.b = b;
    }

    @Override
    public String getValue() {
        return b.getSomethingElse();
    }
}

class PC implements Comparator
     {

    @Override
    public int compare(P o1, P o2) {
        return o1.getValue().compareTo(o2.getValue());
    }

}

    
    
    
             
    
                                                        
    
            
            
    
              
                
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