Do you think it is possible to create something similar to this?
private ArrayList increaseSizeArray(ArrayList array_test, GenericClass) {
array_test.add(new GenericObject()); // instance of GenericClass
return array_test;
}
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4 Answers
Yes, you can.
private static <T> List<T> pushBack(List<T> list, Class<T> typeKey) throws Exception {
list.add(typeKey.getConstructor().newInstance());
return list;
}
Usage example:
List<String> strings = new ArrayList<String>();
pushBack(strings, String.class);
6 Comments
Pierre Guilbert
How do you call that method? I don't know what Class<T> typekey should be. I can't find anything about it. If you have any reading advice, it will be welcome. Thank you for your response!
C. K. Young
@Pierre: Just added a usage example. Basically, if you take a class name (
String in this case) and add .class after it, you have a type key (class object) for that class. String.class has type Class<String>.Pierre Guilbert
I just used it like this: static <T> List<T> pushBack(List<T> list, Class typeKey, int size) and it worked. Thank you, you helped me a lot. Avoiding copy/paste code is always a joy.
Deepak Gangore
Why <T> is used just before return type ? I am also doing the same thing but i want to know the actual usage of <T>. Thanks in advance.
Douglas Held
docs.oracle.com/javase/tutorial/extra/generics/methods.html introduces the construct of
static <T> void method(...) |
Old question but I would imagine this is the preferred way of doing it in java8+
public <T> ArrayList<T> dynamicAdd(ArrayList<T> list, Supplier<T> supplier) {
list.add(supplier.get());
return list;
}
and it could be used like this:
AtomicInteger counter = ...;
ArrayList<Integer> list = ...;
dynamicAdd(list, counter::incrementAndGet);
this will add a number to the list, getting the value from AtomicInteger's incrementAndGet method
Also possible to use constructors as method references like this: MyType::new
Comments
You can do so, and this page in Oracle's docs show you how
// Example of a void method
<T> void doSomething(T someT) {
// Do something with variable
System.out.println(someT.toString());
}
// Example of a method that returns the same generic type passed in.
<T> T getSomeT(T someT) {
return someT;
}
