Local Classes

public class OuterWithLocal {
  public static void staticMethod() {
    class LocalClass {    // local class

    }
  }

  public int instanceMethod() {
    class LocalClass {    // local class

    }

    return -1;
  }
}

local class

A class defined in a method or constructor.

Local classes are defined inside methods or constructors, like local variables.

Local Class Rules

A local class has some interesting features:

• It is visible only within the code block in which it is defined, just like a local variable.

• It can only use final or effectively final method parameters or local variables that are within the same scope.

effectively final

Parameters and variables which are not declared final but whose values never change after initialization.

• A local class has access to fields and methods of the enclosing class, just like a member class does.

• When declared in a static block, local inner classes can access only the static fields and methods of the enclosing class.

• Local classes cannot be declared public, protected, or private, since they are not members of a class.

Practice Exercise

Local classes are commonly used to implement event listeners and other interfaces.

The use of the class can be written right after the definition of the class, making the code more readable.

Local Class Example

package com.example.innerclasses.examples;

// Local Inner Class
public class Outer2 {
  private int outerField;

  public void aMethod() {
    final int localVar = 0;

    class Inner {
      private int innerField; // Can have fields, like
                              // top-level or member class

      public String toString() {
        return "o: " + outerField + " i: " + innerField
            + " l: " + localVar;
      }
    }

    Inner in = new Inner();   // Class used after declared
    System.out.println(in);
  }

  public static void main(String[] args) {
    Outer2 out = new Outer2();
    out.aMethod();
  }
}

Drill

InnerClasses/com.example.innerclasses.drills.PrintSortedPlanetsLocal

• Change this class to use a local class, rather than a member class.

(Solution: PrintSortedPlanetsLocal.java)

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