For example I have a class which starts like this
public class Class<T> {
private ArrayList<Integer> x = new ArrayList<Integer>();
In main when I do
public class Main {
public static void main(String args[]) {
Class x = new Class();
All elements in x should be of Integer type. How can I do something like Class x = new Integer/String ... Class(); So I can specify the type of the objects in x
You mean something like this?
public class MyClass<T>{
private final List<T> x = new ArrayList<T>();
Now your List is of the generic type given to MyClass.
EDIT
OP in comment - if I want to make a fonction which adds elements to x.
In order to do that you need to create a method (rather than function) that takes an item of type T and adds it to x
public void addThing(final T thing) {
x.add(thing);
}
List is the interface and ArrayList is the implementation. You should probably read this.Use Generics.
public class YourClass<T>{
private ArrayList<T> x = new ArrayList<T>();
Then in Main
public class Main{
public static void main(String args[]){
YourClass<Integer> x = new YourClass<Integer>();
}
or
YourClass<String> x = new YourClass<String>();
YourClass<T> could be then an Integer, String, or whatever.
Class<Integer> x = new Class<Integer>();
Don't use names for classes that are already defined in java.lang package.
private ArrayList<T> x = new ArrayList<T>();I think you are confused by Polymorphism and Generics.
What you want:
Class x = new Integer();
is polymorphism. This statement will only be valid if Class is a base class of Integer, which is clearly not the case.
Parent x = new Child();
will work if
class Child extends Parent {
....
}
The class you have written:
public class Class<T> {
private ArrayList<Integer> x = new ArrayList<Integer>();
....
}
is a generic class but you do not use the type parameter. This is not a problem though, your class will still work. When you say:
Class x = new Class();
The type T will simply be Object. But since you do not use this type parameter, it does not have any effect.
To summarize, your statement of:
Class x = new Integer();
will never work as Integer does not have a "is a" relationship with Class. Generics is not used for this purpose.
classClassthis is just confusing.