How can I determine if a Java generic implements a particular interface?
I have tried a few different approaches, but they all results in a "cannot find symbol ... variable T" error.
First Attempt
public abstract class AbstractClass<T> {
public void doFoo() {
if (T instanceof SomeInterface){
// do stuff
}
}
}
Second Attempt
public abstract class AbstractClass<T> {
public void doFoo() {
if (SomeInterface.class.isAssignableFrom(T)) {
// do stuff
}
}
}
Add a constructor taking the class of the object.
public abstract class AbstractClass<T> {
private Class<T> clazz;
public AbstractClass(Class<T> clazz) {
this.clazz = clazz;
}
public void doFoo() {
if (clazz instanceof SomeInterface){
// do stuff
}
}
}
Add a constraint to the type T
with T extends SomeInterface
, thereby restricting the type T
to be a subtype of SomeInterface
.
public abstract class AbstractClass<T extends SomeInterface> {
public void doFoo() {
// do stuff
}
}
Put a bound on it.
public abstract class <T extends SomeInterface> { }
Then you're guaranteed that it will be at least SomeInterface
when passed through as an argument to a method.
From your approach, there's no way to do it, since you don't reference an instance of T
anywhere in your code. If you added an argument to it, you'd be able to at least get further.
public void doFoo(T obj) { }
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