See Also

Use Interface Where Possible refactoring delegates execution of the specified methods, derived from a base class/interface, to an instance of an ancestor class or an inner class, implementing the same interface.

Example

BeforeAfter
// File Class.java
public class Class implements Interface {
    public void publicMethod() {
        ...
    }
    public void hiddenMethod() {
        ...
    }
}
 
// File Class.java UNCHANGED
public class Class implements Interface {
    public void publicMethod() {
        ...
    }
    public void hiddenMethod() {
        ...
    }
}
// File Interface.java
public interface Interface {
    int CONSTANT=0;
    void publicMethod();
}
 
// File Interface.java UNCHANGED
public interface Interface {
    int CONSTANT=0;
    void publicMethod();
}
// File AnotherClass.java
public class AnotherClass {
    Class firstClass;
    Class secondClass;
    public void method() {
        firstClass.publicMethod();
        firstClass.hiddenMethod();
        secondClass.publicMethod();
        if (secondClass instanceof Class) {
            ...
        }
        ...
    }
}
 
// File AnotherClass.java MODIFIED
public class AnotherClass {
    Class firstClass;
    Interface secondInterface;
    public void method() {
        firstClass.publicMethod();
        firstClass.hiddenMethod();
        secondInterface.publicMethod();
        if (secondInterface instanceof Interface) {
            ...
        }
        ...
    }
}
To use interface where possible, follow these steps
  1. Select a class whose methods should be delegated to its parent class or interface. To do that, place the caret on this class in the editor or in the Project Tool Window.
  2. On the main menu or on the context menu of the selection, choose Refactor | Use Interface Where Possible.
  3. In the Use Interface Where Possible dialog box, select the parent object that will replace the usages of the current class.
  4. To replace the current class name in instanceof statements, check the option Use interface/superclass in instanceof.

    Note that if you use instanceof statements and leave this checkbox unselected, you may receive erroneous code, such as:

    if (secondInterface instanceof Class)

    This code will compile, but may produce undesired results.

  5. To review the intended changes and make final corrections prior to the refactoring, click Preview. To continue without preview, click Refactor.

    The Rename variables dialog box appears. It lists the occurrences of the class that may be replaced by the superclass or the interface selected. Select the usages you want to replace, and (optionally) specify new names for each of them.

  6. Click OK to continue. If you have previously clicked the Preview button, the Preview window will appear now.