How to use "Infer Generic Type Arguments..." in Eclipse

Question

Whenever generics are missing from source code in eclipse it suggests I "Infer Generic Type Arguments..."

The problem is that I don't think "Infer Generic Type Arguments..." has ever actually inferred anything. It typically comes up with no suggestions.

What scenarios does it work for? How does it work?

There have been a few cases where it is possible to "infer" something - eclipse still comes up blank.

Answer 1

Here's an example showing how to use "Infer Generic Type Arguments" in eclipse:

First declare a generic class

// GenericFoo.java

public class GenericFoo<T> {
    private T foo;

    public void setFoo(T foo) {
        this.foo = foo;
    }

    public T getFoo() {
       return foo;
    }
}

Then instantiate it without specifying the type, and do an unnecessary type casting.

// GenericFooUsage.java before refactoring

public class GenericFooUsage {

    public GenericFooUsage() {
        GenericFoo foo1 = new GenericFoo<Boolean>();

        foo1.setFoo(new Boolean(true));
        Boolean b = (Boolean)foo1.getFoo();
    }
}

After applying "Infer Generic Type Arguments", the code is refactored as:

// GenericFooUsage.java after refactoring

public class GenericFooUsage {

    public GenericFooUsage() {
        GenericFoo<Boolean> foo1 = new GenericFoo<Boolean>();

        foo1.setFoo(new Boolean(true));
        Boolean b = foo1.getFoo();

       }
}

So what "Infer Generic Type Arguments" does are :

1. automatically infer the type of generic arguments.
2. remove unnecessary type casting.