Add Java implementation of Forward Euler (#518)

Author: atocil

contents/forward_euler_method/code/java/ForwardEuler.java

@@ -0,0 +1,38 @@
+public class ForwardEuler {
+    private static double[] solveEuler(double timestep, int n) {
+        double[] eulerResult = new double[n];
+
+        //Setting the initial condition
+        eulerResult[0] = 1;
+        for(int i = 1; i < eulerResult.length; i++) {
+            eulerResult[i] = eulerResult[i - 1] - (3 * eulerResult[i - 1] * timestep);
+        }
+        return eulerResult;
+    }
+
+    private static boolean checkResult(double[] eulerResult, double threshold, double timestep) {
+        boolean isApprox = true;
+
+        for(int i = 0; i < eulerResult.length; i++) {
+            double time = i * timestep;
+            double solution = Math.exp(-3 * time);
+            if(Math.abs(eulerResult[i] - solution) > threshold) {
+                System.out.println(eulerResult[i] + " " + solution);
+                isApprox = false;
+            }
+        }
+
+        return isApprox;
+    }
+
+    public static void main(String[] args) {
+        double timestep = 0.1;
+        int n = 100;
+        double threshold = 0.1;
+
+        double[] eulerResult = solveEuler(timestep, n);
+        boolean isApprox = checkResult(eulerResult, threshold, timestep);
+
+        System.out.println(isApprox);
+    }
+}

contents/forward_euler_method/forward_euler_method.md

@@ -130,6 +130,8 @@ Full code for the visualization follows:
 [import, lang:"go"](code/golang/euler.go)
 {% sample lang="asm-x64" %}
 [import, lang:"asm-x64"](code/asm-x64/euler.s)
+{% sample lang="java" %}
+[import, lang:"java"](code/java/ForwardEuler.java)
 {% endmethod %}
 
 <script>