CODEWITHSUNDEEP
javaeclipsegenericsrefactoring
billc.cn
billc.cn

Reputation: 7317

Can Eclipse (or any IDE) introduce type parameters to an existing type

This is the exact opposite of how can I remove generic type from class using refactoring.

I want to introduce a type parameter to an interface. It is used quite extensively, so not very practical to do by hand. It is also widely used in import statements and JavaDoc, so a simple global string replace will not work very well either.

Edit:

I did try the "use parent type when possible" refactoring, but it understandably did not work very well at introducing type parameters.

Upvotes: 1

Views: 299

Answers (1)

Mark Peters
Mark Peters

Reputation: 81074

In IntelliJ, you can use the "Change Signature" refactoring. Given this code:

public static void main(String[] args) {
    MyContainer container = new MyContainer("hello!");
    String val = container.get();
    System.out.println(val);
}

class MyContainer {
    final Object value;

    MyContainer(Object value) {
        this.value = value;
    }

    Object get() {
        return value;
    }
}

I right-clicked on MyContainer, then chose Refactor->Change Signature... From here, you can introduce a type parameter T. You need to give a default concrete type for T. Most of the time, to preserve existing code, this would be Object; but it depends on the class you're changing. For example, if MyContainer above used Number instead of Object, the equivalent of the new erasure type would be Number. But you would also need to declare T extends Number in that case.

When I finish this, I get the following:

public static void main(String[] args) {
    MyContainer<Object> container = new MyContainer<Object>("hello!");
    String val = (String) container.get();
    System.out.println(val);
}

class MyContainer<T> {
    final Object value;

    MyContainer(Object value) {
        this.value = value;
    }

    Object get() {
        return value;
    }
}

Now you can start to use T in MyContainer, and by looking at the files that IntelliJ changed, you can start to see where you need to look to start filling in the correct type arguments (since all auto-generated type parameters will be Object).

Upvotes: 2

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