Using Generic Class

Here is a simple class "GenericFoo" that has a
generic paramter "T".

public class GenericFoo<T> {
	
	private T elem;

	public GenericFoo(T elem) {
		super();
		this.elem = elem;
	}

	public T getElem() {
		return elem;
	}

	@Override
	public String toString() {
		return this.elem.toString();
	}
	
}

Variable Without Generics (Incorrect)

Here we incorrectly declare and construct a variable without using generics (we are ingoring the specified generics).

public void useWithoutGenerics()  {
	//Foo has a generic parameter
	//But we ignore it here
	GenericFoo foo = new GenericFoo(10);
	prn(foo);
}

Variable With Generics (Correct)

Here we declare and construct the variable correctly. We pass "Integer" to GenericFoo as the generic parameter.

public void useWithGenerics1()  {
	GenericFoo<Integer> foo;
	foo = new GenericFoo<>(10);
	prn(foo);
}

Using Class Again With Generics (Correctly)

Here we declare and construct the variable correctly. We pass "Integer" to GenericFoo as the generic parameter.

public void useWithGenerics2()  {
	Rectangle rec;
	rec = new Rectangle(10,  5);
	GenericFoo<Rectangle> foo;
	foo = new GenericFoo<>(rec);
	prn(foo);
}

Return Without Generics (Incorrect)

Here we incorrectly declare and construct a variable without using generics (we are ingoring the specified generics).

public GenericFoo getFoo1()  {
	return new GenericFoo(10);
}

Return With Generics (Correct)

Here we correctly declare and construct a variable with using generics.

public GenericFoo<Integer> getFoo2()  {
	return new GenericFoo<>(10);
}

Return Without Generics (Incorrect)

Here we incorrectly declare a method parameter without using generics (we are ingoring the specified generics).

public void printFoo1(GenericFoo foo)  {
	prn(foo);
}

Return With Generics (Correct)

Here we correctly declare a method parameter using generics.

public void printFoo2(GenericFoo<Integer> foo)  {
	prn(foo);
}