JAVA-626: Added 3 articles

core-java-modules/core-java-lang-math/README.md

@@ -10,3 +10,7 @@
 - [Basic Calculator in Java](https://www.baeldung.com/java-basic-calculator)
 - [Overflow and Underflow in Java](https://www.baeldung.com/java-overflow-underflow)
 - [Obtaining a Power Set of a Set in Java](https://www.baeldung.com/java-power-set-of-a-set)
+- [Calculating Logarithms in Java](https://www.baeldung.com/java-logarithms)
+- [Finding Greatest Common Divisor in Java](https://www.baeldung.com/java-greatest-common-divisor)
+- [Calculate Percentage in Java](https://www.baeldung.com/java-calculate-percentage)
+- More articles: [[<-- next]](/../core-java-lang-math-2)

core-java-modules/core-java-lang-math/src/main/java/com/baeldung/algorithms/gcd/GCDImplementation.java

@@ -0,0 +1,55 @@
+package com.baeldung.algorithms.gcd;
+
+public class GCDImplementation {
+
+    public static int gcdByBruteForce(int n1, int n2) {
+        int gcd = 1;
+        for (int i = 1; i <= n1 && i <= n2; i++) {
+            if (n1 % i == 0 && n2 % i == 0) {
+                gcd = i;
+            }
+        }
+        return gcd;
+    }
+
+    public static int gcdByEuclidsAlgorithm(int n1, int n2) {
+        if (n2 == 0) {
+            return n1;
+        }
+        return gcdByEuclidsAlgorithm(n2, n1 % n2);
+    }
+
+    public static int gcdBySteinsAlgorithm(int n1, int n2) {
+        if (n1 == 0) {
+            return n2;
+        }
+
+        if (n2 == 0) {
+            return n1;
+        }
+
+        int n;
+        for (n = 0; ((n1 | n2) & 1) == 0; n++) {
+            n1 >>= 1;
+            n2 >>= 1;
+        }
+
+        while ((n1 & 1) == 0) {
+            n1 >>= 1;
+        }
+
+        do {
+            while ((n2 & 1) == 0) {
+                n2 >>= 1;
+            }
+
+            if (n1 > n2) {
+                int temp = n1;
+                n1 = n2;
+                n2 = temp;
+            }
+            n2 = (n2 - n1);
+        } while (n2 != 0);
+        return n1 << n;
+    }
+}

core-java-modules/core-java-lang-math/src/main/java/com/baeldung/algorithms/percentage/PercentageCalculator.java

@@ -0,0 +1,21 @@
+package com.baeldung.algorithms.percentage;
+
+import java.util.Scanner;
+
+public class PercentageCalculator {
+
+    public double calculatePercentage(double obtained,double total){
+        return obtained*100/total;
+    }
+
+    public static void main(String[] args) {
+        PercentageCalculator pc = new PercentageCalculator();
+        Scanner in = new Scanner(System.in);
+        System.out.println("Enter obtained marks:");
+        double obtained = in.nextDouble();
+        System.out.println("Enter total marks:");
+         double total =in.nextDouble();
+        System.out.println("Percentage obtained :"+pc.calculatePercentage(obtained,total));
+    }
+
+}

core-java-modules/core-java-lang-math/src/test/java/com/baeldung/algorithms/gcd/GCDImplementationUnitTest.java

@@ -0,0 +1,32 @@
+package com.baeldung.algorithms.gcd;
+
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class GCDImplementationUnitTest {
+
+    @Test
+    public void whenCalculatingGCDByBruteForceMethod_thenCorrect() {
+        int n1 = 60;
+        int n2 = 90;
+        int gcd = GCDImplementation.gcdByBruteForce(n1, n2);
+        assertThat(gcd).isEqualTo(30);
+    }
+
+    @Test
+    public void whenCalculatingGCDByEuclidsAlgorithm_thenCorrect() {
+        int n1 = 60;
+        int n2 = 90;
+        int gcd = GCDImplementation.gcdByEuclidsAlgorithm(n1, n2);
+        assertThat(gcd).isEqualTo(30);
+    }
+
+    @Test
+    public void whenCalculatingGCDBySteinsAlgorithm_thenCorrect() {
+        int n1 = 60;
+        int n2 = 90;
+        int gcd = GCDImplementation.gcdBySteinsAlgorithm(n1, n2);
+        assertThat(gcd).isEqualTo(30);
+    }
+}

core-java-modules/core-java-lang-math/src/test/java/com/baeldung/algorithms/logarithm/LogarithmUnitTest.java

@@ -0,0 +1,31 @@
+package com.baeldung.algorithms.logarithm;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.Test;
+
+public class LogarithmUnitTest {
+
+    @Test
+    public void givenLog10_shouldReturnValidResults() {
+        assertEquals(Math.log10(100), 2);
+        assertEquals(Math.log10(1000), 3);
+    }
+
+    @Test
+    public void givenLogE_shouldReturnValidResults() {
+        assertEquals(Math.log(Math.E), 1);
+        assertEquals(Math.log(10), 2.30258, 0.00001);
+    }
+
+    @Test
+    public void givenCustomLog_shouldReturnValidResults() {
+        assertEquals(customLog(2, 256), 8);
+        assertEquals(customLog(10, 100), 2);
+    }
+
+    private static double customLog(double base, double logNumber) {
+        return Math.log(logNumber) / Math.log(base);
+    }
+
+}

core-java-modules/core-java-lang-math/src/test/java/com/baeldung/algorithms/percentage/PercentageCalculatorUnitTest.java

@@ -0,0 +1,33 @@
+package com.baeldung.algorithms.percentage;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class PercentageCalculatorUnitTest {
+    private PercentageCalculator pc = new PercentageCalculator();
+
+    @Test
+    public void whenPass2Integers_thenShouldCalculatePercentage(){
+        Assert.assertEquals("Result not as expected",
+                50.0,pc.calculatePercentage(50,100),0.1);
+    }
+
+    @Test
+    public void whenPassObtainedMarksAsDouble_thenShouldCalculatePercentage(){
+        Assert.assertEquals("Result not as expected",5.05,
+                pc.calculatePercentage(50.5,1000),0.1);
+    }
+
+    @Test
+    public void whenPassTotalMarksAsDouble_thenShouldCalculatePercentage(){
+        Assert.assertEquals("Result not as expected",19.6,
+                pc.calculatePercentage(5,25.5),0.1);
+    }
+
+    @Test
+    public void whenPass2DoubleNumbers_thenShouldCalculatePercentage(){
+        Assert.assertEquals("Result not as expected",20,
+                pc.calculatePercentage(5.5,27.5),0.1);
+    }
+
+}