Java Language Tutorial => Instantiating a generic type

Example

Due to type erasure the following will not work:

public <T> void genericMethod() {
    T t = new T(); // Can not instantiate the type T.
}

The type T is erased. Since, at runtime, the JVM does not know what T originally was, it does not know which constructor to call.

Workarounds

Passing T's class when calling genericMethod:

public <T> void genericMethod(Class<T> cls) {
    try {
        T t = cls.newInstance();
    } catch (InstantiationException | IllegalAccessException e) {
         System.err.println("Could not instantiate: " + cls.getName());
    }
}

genericMethod(String.class);

Which throws exceptions, since there is no way to know if the passed class has an accessible default constructor.

Java SE 8

Passing a reference to T's constructor:

public <T> void genericMethod(Supplier<T> cons) {
    T t = cons.get();
}

genericMethod(String::new);

PDF - Download Java Language for free

Previous Next

Java Language

Fastest Entity Framework Extensions

Example

Workarounds

Got any Java Language Question?

Java Language

Java Language Generics Instantiating a generic type

Fastest Entity Framework Extensions

Example

Workarounds

Got any Java Language Question?