From 57fa6b05bb169fb3f768e6ea2c98047eab300932 Mon Sep 17 00:00:00 2001
From: CDsigma <cdsigma271@gmail.com>
Date: Wed, 19 Sep 2018 18:49:09 -0700
Subject: [PATCH] Added Forward Euler in Java

---
 .../forward_euler_method/code/java/Euler.java | 52 +++++++++++++++++++
 .../forward_euler_method.md                   |  2 +
 2 files changed, 54 insertions(+)
 create mode 100644 contents/forward_euler_method/code/java/Euler.java

diff --git a/contents/forward_euler_method/code/java/Euler.java b/contents/forward_euler_method/code/java/Euler.java
new file mode 100644
index 000000000..7c9340c02
--- /dev/null
+++ b/contents/forward_euler_method/code/java/Euler.java
@@ -0,0 +1,52 @@
+public class ForwardEuler {
+  
+  public static double[] append(double[] oldArray, double newItem) {
+    double[] newArray = new double[oldArray.length + 1];
+
+    for(int i = 0; i < oldArray.length; i++) {
+        newArray[i] = oldArray[i];
+    }
+    newArray[newArray.length - 1] = newItem;
+
+    return newArray;
+}
+  
+  public static double[] solveEuler(double timeStep, int n) {
+    double[] result = {1};
+
+    for(int i = 0; i < n; i++) {
+      result = append(result, result[i] - 3 * result[i] * timeStep);
+    }
+
+    return result;
+  }
+  
+  public static boolean checkResult(double[] result, double threshold, double timeStep) {
+    boolean isApprox = true;
+
+    for(int i = 0; i < result.length; i++) {
+        double solution = Math.pow(Math.E, -3 * i * timeStep);
+      
+        if(Math.abs(result[i] - solution) > threshold) {
+            isApprox = false;
+        }
+    }
+
+    return isApprox;
+}
+
+  public static void main(String[] args) {
+    double timeStep = 0.01;
+    int n = 100;
+    double threshold = 0.01;
+    
+    double[] result = solveEuler(timeStep, n);
+    boolean isApprox = checkResult(result, threshold, timeStep);
+
+    if(isApprox) {
+        System.out.print("All values within threshold");
+    } else {
+        System.out.print("Value(s) not in threshold");
+    } 
+  }
+}
diff --git a/contents/forward_euler_method/forward_euler_method.md b/contents/forward_euler_method/forward_euler_method.md
index 25210e1d1..789f79e1e 100644
--- a/contents/forward_euler_method/forward_euler_method.md
+++ b/contents/forward_euler_method/forward_euler_method.md
@@ -121,6 +121,8 @@ Full code for the visualization follows:
 [import, lang:"matlab"](code/matlab/euler.m)
 {% sample lang="swift" %}
 [import, lang:"swift"](code/swift/euler.swift)
+{% sample lang="java" %}
+[import, lang:"java"](code/java/Euler.java)
 {% endmethod %}
 
 <script>