This gist illustrates implementation of the strategy pattern using an enum.

enumStrategyPatternTest.java

import org.apache.commons.lang.math.RandomUtils;
import org.testng.Assert;
import org.testng.annotations.Test;

public class enumStrategyPatternTest() {
    
    public enum Strategy {
        ADD {
            @Override
            public int execute(int a, int b) {
                return a + b;
            }
        },
        SUBTRACT {
            @Override
            public int execute(int a, int b) {
                return a - b;
            }
        },
        MULTIPLY {
            @Override
            public int execute(int a, int b) {
                return a * b;
            }
        },
        DIVIDE {
            @Override
            public int execute(int a, int b) {
                return a / b;
            }
        };
    
        public abstract int execute(int a, int b);
    }
    
    @Test
    public void strategyPatternWorksWithEnum() {
        int a = RandomUtils.nextInt();
        int b = RandomUtils.nextInt();
    
        Assert.assertTrue(Strategy.ADD.execute(a, b) == a + b);
        Assert.assertTrue(Strategy.SUBTRACT.execute(a, b) == a - b);
        Assert.assertTrue(Strategy.MULTIPLY.execute(a, b) == a * b);
        Assert.assertTrue(Strategy.DIVIDE.execute(a, b) == a / b);
    }
    
}