Inital commit of exercise 1

.classpath

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+<?xml version="1.0" encoding="UTF-8"?>
+<classpath>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.8"/>
+	<classpathentry kind="src" path="src"/>
+	<classpathentry kind="output" path="bin"/>
+</classpath>

.project

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<projectDescription>
+  <name>ALGUE2</name>
+  <comment/>
+  <projects>
+    </projects>
+  <buildSpec>
+    <buildCommand>
+      <name>org.eclipse.jdt.core.javabuilder</name>
+      <arguments>
+            </arguments>
+    </buildCommand>
+  </buildSpec>
+  <natures>
+    <nature>org.eclipse.jdt.core.javanature</nature>
+  </natures>
+</projectDescription>

.settings/org.eclipse.jdt.core.prefs

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+eclipse.preferences.version=1
+org.eclipse.jdt.core.compiler.codegen.inlineJsrBytecode=enabled
+org.eclipse.jdt.core.compiler.codegen.targetPlatform=1.8
+org.eclipse.jdt.core.compiler.compliance=1.8
+org.eclipse.jdt.core.compiler.problem.assertIdentifier=error
+org.eclipse.jdt.core.compiler.problem.enumIdentifier=error
+org.eclipse.jdt.core.compiler.source=1.8

.vscode/launch.json

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+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "type": "java",
+            "name": "Debug (Launch) - Current File",
+            "request": "launch",
+            "mainClass": "${file}"
+        },
+        {
+            "type": "java",
+            "name": "Debug (Launch)-App<ALGUE2>",
+            "request": "launch",
+            "mainClass": "app.App",
+            "projectName": "ALGUE2"
+        }
+    ]
+}

src/app/App.java

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+package app;
+
+public class App {
+    public static void main(String[] args) throws Exception {
+        /** Aufgabe 1.1 - 1.3 */
+        System.out.println("++++ Aufgabe 1.1 - 1.3 ++++");
+        MyStack<String> stack = new MyStack<String>();
+        stack.push("hello");
+        stack.push("world");
+        stack.push("123");
+        System.out.println(stack.pop());
+        System.out.println(stack.pop());
+        System.out.println(stack.pop());
+
+        /** Aufgabe 1.4 */
+        System.out.println("++++ Aufgabe 1.4 ++++");
+        tokenizeAndCalc("( 2 + 3 )");
+        tokenizeAndCalc("( 3 - ( 2 * 3 ) )");
+        tokenizeAndCalc("( ( 5 * 4 ) - ( 2 * ( 3 / 4 ) ) )");
+    }
+
+    private static void tokenizeAndCalc(String in) {
+        MyStack<String> stack = new MyStack<String>();
+        int i = 0;
+        while (i < in.length()) {
+            String a = "";
+            // Catch last case if space is missing
+            if (i + 1 == in.length())
+                a = "" + in.charAt(i);
+            else
+                while (in.charAt(i) != ' ') {
+                    a = a + in.charAt(i);
+                    i++;
+                }
+            stack.push(a);
+            i++;
+        }
+        stack.reverse(); // Reverse stack due to limitations
+
+        MyStack<String> opStack = new MyStack<String>();
+        MyStack<Float> numStack = new MyStack<Float>();
+        while (!stack.isEmpty()) {
+            String curr = stack.pop();
+            if (curr.matches("-?\\d+"))
+                numStack.push(Float.parseFloat(curr));
+            else if (curr.matches("\\*|\\+|\\-|\\/"))
+                opStack.push(curr);
+            else if (curr.equals(")")) {
+                String currOp = opStack.pop();
+                float num1 = numStack.pop();
+                float num2 = numStack.pop();
+                switch (currOp) {
+                case "+":
+                    numStack.push(num2 + num1);
+                    break;
+                case "-":
+                    numStack.push(num2 - num1);
+                    break;
+                case "*":
+                    numStack.push(num2 * num1);
+                    break;
+                case "/":
+                    numStack.push(num2 / num1);
+                    break;
+                }
+            }
+        }
+        System.out.println(in);
+        System.out.println("Ergebnis: " + numStack.pop());
+    }
+
+}

src/app/MyStack.java

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+package app;
+
+import java.util.Arrays;
+
+@SuppressWarnings("unchecked")
+public class MyStack<E> {
+    private E[] array;
+    private int pointer = 0;
+
+    public MyStack() {
+        this.array = (E[]) new Object[1];
+    }
+
+    public void push(E el) {
+        if (array.length == pointer)
+            resizeArray(1);
+        array[pointer++] = el;
+    }
+
+    public E pop() {
+        pointer--;
+        E ret = array[pointer];
+        if (array.length >= pointer)
+            resizeArray(0);
+        return ret;
+    }
+
+    private void resizeArray(int factor) {
+        E[] old = this.array.clone();
+        this.array = (E[]) new Object[pointer + factor];
+        int i = 0;
+        for (E e : old)
+            if (pointer + factor > i)
+                this.array[i++] = e;
+    }
+
+    public boolean isEmpty() {
+        return this.array.length == 0;
+    }
+
+    @Override
+    public String toString() {
+        return Arrays.toString(this.array);
+    }
+
+    public void reverse() {
+        E[] old = this.array.clone();
+        int ii = 0;
+        for (int i = this.array.length - 1; i > -1; i--)
+            this.array[i] = old[ii++];
+    }
+}