Interface

Here is the interface
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public interface Ithing{
    public String getName();
    public String getType();
}
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Here is the class that implemnts the interface
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class TheRealThing implements Ithing{

    public String getName(){return "coke";}
    public String getType(){return "soft drink";}
}
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Here is the class that is decoupled from 
TheRealThing. This class need not change when a different
implementation of Ithing is provided.
Notice there are only references to the Ithing interface.
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class Decoupled{

    Ithing thing = null;
    
    public void setThing(Ithing thing){
        this.thing = thing;
    }

    public void  getThingDetails(){
        if(thing!=null){
            System.out.println(thing.getName());
            System.out.println(thing.getType());
        }
    }

}
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This is a test stub to run everything.
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class Test{

    public static void main(String[] args){
        System.out.println("class: Test, method: main");

        Decoupled decoupled = new Decoupled();
        TheRealThing aThing = new TheRealThing();
        decoupled.setThing(aThing);
        decoupled.getThingDetails();
    }

}
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Here is a tar with the above java classes in it.
interface.tar