Create instance of generic type in Java?

You are correct. You can't do new E(). But you can change it to

private static class SomeContainer<E> {    E createContents(Class<E> clazz) {        return clazz.newInstance();    }}

It's a pain. But it works. Wrapping it in the factory pattern makes it a little more tolerable.

I don't know if this helps, but when you subclass (including anonymously) a generic type, the type information is available via reflection. e.g.,

public abstract class Foo<E> {  public E instance;    public Foo() throws Exception {    instance = ((Class)((ParameterizedType)this.getClass().       getGenericSuperclass()).getActualTypeArguments()[0]).newInstance();    ...  }}

So, when you subclass Foo, you get an instance of Bar e.g.,

// notice that this in anonymous subclass of Fooassert( new Foo<Bar>() {}.instance instanceof Bar );

But it's a lot of work, and only works for subclasses. Can be handy though.

In Java 8 you can use the Supplier functional interface to achieve this pretty easily:

class SomeContainer<E> {  private Supplier<E> supplier;  SomeContainer(Supplier<E> supplier) {    this.supplier = supplier;  }  E createContents() {    return supplier.get();  }}

You would construct this class like this:

SomeContainer<String> stringContainer = new SomeContainer<>(String::new);

The syntax String::new on that line is a constructor reference.

If your constructor takes arguments you can use a lambda expression instead:

SomeContainer<BigInteger> bigIntegerContainer    = new SomeContainer<>(() -> new BigInteger(1));