StreamPost

IsPerfectSquare.java

import java.util.function.Predicate;

public class IsPerfectSquare implements Predicate<Integer> {
    @Override
    public boolean test(Integer x) {
        return Math.floor(Math.sqrt(x)) == Math.sqrt(x);
    }
}

IsPerfectSquareTest.java

import org.testng.annotations.BeforeClass;
import org.testng.annotations.Test;

import static org.testng.Assert.assertFalse;
import static org.testng.Assert.assertTrue;

public class IsPerfectSquareTest {

    private IsPerfectSquare isPerfectSquare;

    @BeforeClass
    public void setUp() {
        isPerfectSquare = new IsPerfectSquare();
    }

    @Test
    public void shouldReturnTrueForPerfectSquare() {
        assertTrue(isPerfectSquare.test(81));
        assertTrue(isPerfectSquare.test(36));
    }

    @Test
    public void shouldReturnFalseIfNumberIsNotPerfectSquare() {
        assertFalse(isPerfectSquare.test(8));
        assertFalse(isPerfectSquare.test(15));
    }

}

MultiplyBy3.java

import java.util.function.Function;

public class MultiplyBy3 implements Function<Integer, Integer> {
    @Override
    public Integer apply(Integer x) {
        return x * 3;
    }
}

OddFilterIn.java

import java.util.function.Predicate;

public class OddFilterIn implements Predicate<Integer> {
    @Override
    public boolean test(Integer x) {
        return x % 2 != 0;
    }
}