Java Example

• adapters

  • adapters/SquarePegAdapter.java

    package refactoring_guru.adapter.example.adapters;
    
    import refactoring_guru.adapter.example.round.RoundPeg;
    import refactoring_guru.adapter.example.square.SquarePeg;
    
    /**
     * Adapter allows fitting square pegs into round holes.
    */
    public class SquarePegAdapter extends RoundPeg {
        private SquarePeg peg;
    
        public SquarePegAdapter(SquarePeg peg) {
            this.peg = peg;
        }
    
        @Override
        public double getRadius() {
            double result;
            // Calculate a minimum circle radius, which can fit this peg.
            result = (Math.sqrt(Math.pow((peg.getWidth() / 2), 2) * 2));
            return result;
        }
    }

• round

  • round/RoundHole.java

    package refactoring_guru.adapter.example.round;
    
    /**
     * RoundHoles are compatible with RoundPegs.
    */
    public class RoundHole {
        private double radius;
    
        public RoundHole(double radius) {
            this.radius = radius;
        }
    
        public double getRadius() {
            return radius;
        }
    
        public boolean fits(RoundPeg peg) {
            boolean result;
            result = (this.getRadius() >= peg.getRadius());
            return result;
        }
    }

  • round/RoundPeg.java

    package refactoring_guru.adapter.example.round;
    
    /**
     * RoundPegs are compatible with RoundHoles.
    */
    public class RoundPeg {
        private double radius;
    
        public RoundPeg() {}
    
        public RoundPeg(double radius) {
            this.radius = radius;
        }
    
        public double getRadius() {
            return radius;
        }
    }

• square

  • square/SquarePeg.java

    package refactoring_guru.adapter.example.square;
    
    /**
     * SquarePegs are not compatible with RoundHoles (they were implemented by
    * previous development team). But we have to integrate them into our program.
    */
    public class SquarePeg {
        private double width;
    
        public SquarePeg(double width) {
            this.width = width;
        }
    
        public double getWidth() {
            return width;
        }
    
        public double getSquare() {
            double result;
            result = Math.pow(this.width, 2);
            return result;
        }
    }

• Demo.java

package refactoring_guru.adapter.example;

import refactoring_guru.adapter.example.adapters.SquarePegAdapter;
import refactoring_guru.adapter.example.round.RoundHole;
import refactoring_guru.adapter.example.round.RoundPeg;
import refactoring_guru.adapter.example.square.SquarePeg;

/**
 * Somewhere in client code...
 */
public class Demo {
    public static void main(String[] args) {
        // Round fits round, no surprise.
        RoundHole hole = new RoundHole(5);
        RoundPeg rpeg = new RoundPeg(5);
        if (hole.fits(rpeg)) {
            System.out.println("Round peg r5 fits round hole r5.");
        }

        SquarePeg smallSqPeg = new SquarePeg(2);
        SquarePeg largeSqPeg = new SquarePeg(20);
        // hole.fits(smallSqPeg); // Won't compile.

        // Adapter solves the problem.
        SquarePegAdapter smallSqPegAdapter = new SquarePegAdapter(smallSqPeg);
        SquarePegAdapter largeSqPegAdapter = new SquarePegAdapter(largeSqPeg);
        if (hole.fits(smallSqPegAdapter)) {
            System.out.println("Square peg w2 fits round hole r5.");
        }
        if (!hole.fits(largeSqPegAdapter)) {
            System.out.println("Square peg w20 does not fit into round hole r5.");
        }
    }
}

Round peg r5 fits round hole r5.
Square peg w2 fits round hole r5.
Square peg w20 does not fit into round hole r5.