Add twin prime (#3312)

src/main/java/com/thealgorithms/maths/TwinPrime.java

@@ -0,0 +1,32 @@
+package com.thealgorithms.maths;
+/*
+ * Java program to find 'twin prime' of a prime number
+ * Twin Prime: Twin prime of a number n is (n+2) 
+ * if and only if n & (n+2) are prime.
+ * Wikipedia: https://en.wikipedia.org/wiki/Twin_prime
+ * 
+ * Author: Akshay Dubey (https://github.com/itsAkshayDubey)
+ * 
+ * */
+
+public class TwinPrime {
+	
+	/**
+     * This method returns twin prime of the integer value passed as argument
+     *
+     * @param input_number Integer value of which twin prime is to be found
+     * @return (number + 2) if number and (number + 2) are prime, -1 otherwise
+     */
+	static int getTwinPrime(int inputNumber) {
+		
+		//if inputNumber and (inputNumber + 2) are both prime 
+		//then return (inputNumber + 2) as a result
+		if(PrimeCheck.isPrime(inputNumber) && PrimeCheck.isPrime(inputNumber + 2) ) {
+			return inputNumber + 2;
+		}
+		//if any one from inputNumber and (inputNumber + 2) or if both of them are not prime 
+		//then return -1 as a result
+		return -1;
+	}
+
+}

src/test/java/com/thealgorithms/maths/TwinPrimeTest.java

@@ -0,0 +1,60 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+class TwinPrimeTest {
+
+	@Test
+	void shouldReturn7() {
+		//given
+		int number = 5;
+		int expectedResult = 7;
+		
+		//when
+		int actualResult = TwinPrime.getTwinPrime(number);
+		
+		//then
+		assertEquals(expectedResult,actualResult);
+	}
+	
+	@Test
+	void shouldReturn5() {
+		//given
+		int number = 3;
+		int expectedResult = 5;
+		
+		//when
+		int actualResult = TwinPrime.getTwinPrime(number);
+		
+		//then
+		assertEquals(expectedResult,actualResult);
+	}
+	
+	@Test
+	void shouldReturnNegative1() {
+		//given
+		int number = 4;
+		int expectedResult = -1;
+		
+		//when
+		int actualResult = TwinPrime.getTwinPrime(number);
+		
+		//then
+		assertEquals(expectedResult,actualResult);
+	}
+	
+	@Test
+	void shouldReturn19() {
+		//given
+		int number = 17;
+		int expectedResult = 19;
+		
+		//when
+		int actualResult = TwinPrime.getTwinPrime(number);
+		
+		//then
+		assertEquals(expectedResult,actualResult);
+	}
+}