How to add generic object to list in java?

Question

How to add a generic object to list in java?

Currently, I have two classes doing the same function and would like to integrate them together

public class MyClass1 {
    private List<Object1> myList = new ArrayList<>();

    public void addList(Object1 o) {
        myList.add(o);
    }
} 

public class MyClass2 {
    private List<Object2> myList = new ArrayList<>();

    public void addList(Object2 o) {
        myList.add(o);
}
}

something like

public class MyClass {
    private List<Object> myList = new ArrayList<>();

    public void addList(Object o) {
        myList.add(o);
    }
}

Mureinik · Accepted Answer · 2019-04-01 13:55:10Z

3

You could make your own class generic:

public class MyClass<T> {
    private List<T> myList = new ArrayList<>();

    public void addList(T o) {
        myList.add(o);
    }
}

answered Apr 1, 2019 at 13:55

Mureinik

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Sebastian Siemens · Accepted Answer · 2019-04-01 13:57:38Z

1

You can make both classes Object1 and Object2 implement the same interface 'ObjInterface'

public class MyClass {
    private List<ObjInterface> myList = new ArrayList<>();

    public void addList(ObjInterface o) {
        myList.add(o);
    }
}

answered Apr 1, 2019 at 13:57

Sebastian Siemens

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Comments

Sean Van Gorder · Accepted Answer · 2019-04-01 20:50:42Z

1

If you want the class to contain only Object1 or only Object2 and never anything else, you can combine the other two answers:

interface ObjInterface {
    // may be empty
}

public class MyClass<T extends ObjInterface> {
    private List<T> myList = new ArrayList<>();

    public void addList(T o) {
        myList.add(o);
    }
}

MyClass<Object1> object1only = new MyClass<>();
MyClass<Object2> object2only = new MyClass<>();

and add implements ObjInterface to the definitions of Object1 and Object2.

If you add methods common to both classes to ObjInterface, you can call those methods on the T objects in MyClass, since they're guaranteed to be a subclass of ObjInterface.

answered Apr 1, 2019 at 20:50

Sean Van Gorder

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