baeldung-articles : BAEL - 6856 (#15693)

Calculating the Power of a Number in Java Without Using Math pow() Method (commit)

core-java-modules/core-java-lang-math-3/src/test/java/com/baeldung/com.baeldung.powerinsteadofmathpow/FindPowerInsteadOfUsingMathPowUnitTest.java

@@ -0,0 +1,57 @@
+package com.baeldung.powerinsteadofmathpow;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class FindPowerInsteadOfUsingMathPowUnitTest {
+    double result = 1;
+    double base = 2;
+    int exponent = 3;
+
+    @Test
+    public void givenBaseAndExponentNumbers_whenUtilizingIterativeApproach_thenReturnThePower() {
+
+        for (int i = 0; i < exponent; i++) {
+            result *= base;
+        }
+
+        assertEquals(8, result);
+    }
+
+    @Test
+    public void givenBaseAndExponentNumbers_whenUtilizingRecursionApproach_thenReturnThePower() {
+
+        result = calculatePowerRecursively(base, exponent);
+
+        assertEquals(8, result);
+    }
+
+    private double calculatePowerRecursively(double base, int exponent) {
+        if (exponent == 0) {
+            return 1;
+        } else {
+            return base * calculatePowerRecursively(base, exponent - 1);
+        }
+    }
+
+    @Test
+    public void givenBaseAndExponentNumbers_whenUtilizingFastApproach_thenReturnThePower() {
+        result = calculatePowerFast(base, exponent);
+
+        assertEquals(8, result);
+    }
+
+    private double calculatePowerFast(double base, int exponent) {
+        if (exponent == 0) {
+            return 1;
+        }
+
+        double halfPower = calculatePowerFast(base, exponent / 2);
+        if (exponent % 2 == 0) {
+            return halfPower * halfPower;
+        } else {
+            return base * halfPower * halfPower;
+        }
+    }
+}