Replace inheritance with delegation

The Replace Inheritance With Delegation refactoring lets you remove a class from inheritance hierarchy, while preserving the functionality of the parent. IntelliJ IDEA creates a private inner class that inherits the former superclass or interface. Selected methods of the parent are invoked via the new inner class.

Select a class you want to refactor.
From the main menu, or from the context menu, select Refactor | Replace Inheritance With Delegation.
In the dialog that opens, specify the parent object, the name of the inner class definition. Also, select the members of the parent class that will be delegated through the inner class, and getter options.
Preview and apply changes.

Example

Before	After
// File Class.java public class Class extends SuperClass { public int varInt; public void openMethod() { ... } } // File SuperClass.java public abstract class SuperClass { public static final int CONSTANT=0; public abstract void openMethod(); public void secretMethod() { ... } }	// File Class.java public class Class { public int varInt; private final MySuperClass superClass = new MySuperClass(); public SuperClass getSuperClass() { return superClass; } public void openMethod() { superClass.openMethod(); } private class MySuperClass extends SuperClass { public void openMethod() { ... } } } // File SuperClass.java UNCHANGED public abstract class SuperClass { public static final int CONSTANT=0; public abstract void openMethod(); public void secretMethod() { ... } }

Before

After

// File Class.java
public class Class extends SuperClass {
    public int varInt;
    public void openMethod() {
        ...
    }
}

// File SuperClass.java
public abstract class SuperClass {
    public static final int CONSTANT=0;
    public abstract void openMethod();
    public void secretMethod() {
        ...
    }
}

// File Class.java
public class Class {
    public int varInt;
    private final MySuperClass superClass = new MySuperClass();
    public SuperClass getSuperClass() {
        return superClass;
    }
    public void openMethod() {
        superClass.openMethod();
    }
    private class MySuperClass extends SuperClass {
        public void openMethod() {
            ...
        }
    }
}

// File SuperClass.java UNCHANGED
public abstract class SuperClass {
    public static final int CONSTANT=0;
    public abstract void openMethod();
    public void secretMethod() {
        ...
    }
}

Replace inheritance with delegation dialog

Use this dialog to specify options for the Replace Inheritance With Delegation refactoring.

Item	Description
Replace with delegation inheritance from	Select here the parent object, inheritance to which will be replaced.
Field name	Specify the name for the field of the new inner class.
Inner class name	In this field specify the name for the inner class definition.
Delegate members	In this area, select the members of the parent class, that will be delegated through the inner class.
Generate getter for delegated component	Check this option to create a getter for the inner class.

Last modified: 24 August 2023