Instantiating object of same class from within class in java

Question

I have an abstract class that has a shared method which creates a new instance of that class. I don't want to make a new instance of the actual abstract class (you can't do that anyway) but of the implementing subclass.

In order to do it I'm doing this:

constructor = this.getClass().getConstructor(String.class,String.class);
                    Object[] params = new Object[2];
                    params[0] = "one";
                    params[1]= "two";

                    Object piece = constructor.newInstance(params);

Is there a less wordy way to do this

Unless you're looking at DI frameworks like Spring or Weld, I don't think there's a better way to do this. Constructors are specific to the implementing class, and cannot be generalized via interfaces. If you don't like this pattern, might I suggest you create a "newInstance" method that returns the abstract type. That would bring subclasses into an interface contract for instantiation. — SplinterReality
– SplinterReality, Commented Apr 4, 2011 at 1:23

WhiteFang34 · Accepted Answer · 2011-04-04 01:23:30Z

4

While you could write what you're doing with a little less code, I think there's probably a cleaner way you should consider. You could make an abstract method that extending classes have to implement to construct a new instance. That'll guarantee there's always a safe constructor to call and no instantiation exceptions to deal with either. It'd look something like this for your case:

public abstract class AbstractClass {
    protected abstract AbstractClass newInstance(String str1, String str2);

    public void foo() {
        Object piece = newInstance("one", "two");
    }
}

public class MyClass extends AbstractClass {
    protected AbstractClass newInstance(String str1, String str2) {
        return new MyClass(str1, str2);
    }
}

answered Apr 4, 2011 at 1:23

WhiteFang34

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Ernest Friedman-Hill · Accepted Answer · 2011-04-04 01:24:17Z

2

I would probably write

constructor = this.getClass().getConstructor(String.class,String.class);
Object piece = constructor.newInstance(new String[] {"one", "two"});

answered Apr 4, 2011 at 1:24

Ernest Friedman-Hill

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