Vorlesung 13 / Aufgabe 1

VL13/Aufgabe01/Aufgabe01.java

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+package VL13.Aufgabe01;
+
+import java.util.Stack;
+
+public class Aufgabe01 {
+  public static void main(String[] args) {
+
+    // Integer Stack
+    System.out.printf("\n%s:\n", "Integer Stack");
+
+    IntegerStack integerStack = new IntegerStack();
+    integerStack.push(7);
+    integerStack.push(3);
+    integerStack.push(8);
+    integerStack.push(2);
+    System.out.println(integerStack.pop());
+    System.out.println(integerStack.pop());
+    integerStack.push(7);
+    System.out.println(integerStack.pop());
+    System.out.println(integerStack.pop());
+
+    // Generic Stack (Integer)
+    System.out.printf("\n%s:\n", "Generic Stack (Integer)");
+
+    GenericStack<Integer> gIntegerStack = new GenericStack<Integer>();
+    gIntegerStack.push(7);
+    gIntegerStack.push(3);
+    gIntegerStack.push(8);
+    gIntegerStack.push(2);
+    System.out.println(gIntegerStack.pop());
+    System.out.println(gIntegerStack.pop());
+    gIntegerStack.push(7);
+    System.out.println(gIntegerStack.pop());
+    System.out.println(gIntegerStack.pop());
+
+    // Generic Stack (String)
+    System.out.printf("\n%s:\n", "Generic Stack (String)");
+
+    GenericStack<String> gStringStack = new GenericStack<String>();
+    gStringStack.push("Hallo");
+    gStringStack.push("Welt");
+    gStringStack.push("!");
+
+    System.out.println(gStringStack.pop());
+    System.out.println(gStringStack.pop());
+    System.out.println(gStringStack.pop());
+
+    // Stack (Integer)
+    System.out.printf("\n%s:\n", "Stack (Integer)");
+
+    Stack<Integer> nIntegerStack = new Stack<Integer>();
+    nIntegerStack.push(7);
+    nIntegerStack.push(3);
+    nIntegerStack.push(8);
+    nIntegerStack.push(2);
+    System.out.println(nIntegerStack.pop());
+    System.out.println(nIntegerStack.pop());
+    nIntegerStack.push(7);
+    System.out.println(nIntegerStack.pop());
+    System.out.println(nIntegerStack.pop());
+
+    // Stack (String)
+    System.out.printf("\n%s:\n", "Stack (String)");
+
+    Stack<String> stringStack = new Stack<String>();
+    stringStack.push("Hallo");
+    stringStack.push("Welt");
+    stringStack.push("!");
+
+    System.out.println(stringStack.pop());
+    System.out.println(stringStack.pop());
+    System.out.println(stringStack.pop());
+  }
+}

VL13/Aufgabe01/GenericStack.java

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+package VL13.Aufgabe01;
+
+/**
+ * A generic stack.
+ */
+public class GenericStack<T> {
+  StackItem<T> start;
+
+  /**
+   * A stack item to store a single item on the stack.
+   */
+  private class StackItem<E> {
+    E value;
+    StackItem<E> next;
+    StackItem<E> prev;
+
+    StackItem(E value) {
+      this.value = value;
+    }
+  }
+
+  /**
+   * Method to push a value to the stack.
+   *
+   * @param value The value to store on the stack.
+   */
+  public void push(T value) {
+    if (start == null) {
+      start = new StackItem<T>(value);
+    } else {
+      StackItem<T> item = start;
+
+      // get the last item of the stack.
+      while (item.next != null) {
+        item = item.next;
+      }
+
+      // create a new stack item to store the value.
+      item.next = new StackItem<T>(value);
+      item.next.prev = item;
+    }
+  }
+
+  /**
+   * Method to pop a value from the stack.
+   *
+   * @return The value from stack.
+   */
+  public T pop() {
+    StackItem<T> item = start;
+
+    // get the last item of the stack.
+    while (item.next != null) {
+      item = item.next;
+    }
+
+    // remove last item from stack.
+    if (item.prev == null) {
+      start = null;
+    } else {
+      item.prev.next = null;
+    }
+
+    // return the value of the last item of the stack.
+    return item.value;
+  }
+}

VL13/Aufgabe01/IntegerStack.java

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+package VL13.Aufgabe01;
+
+/**
+ * A integer stack.
+ */
+public class IntegerStack {
+  StackItem start;
+
+  private class StackItem {
+    int value;
+    StackItem next;
+    StackItem prev;
+
+    StackItem(int value) {
+      this.value = value;
+    }
+  }
+
+  /**
+   * Method to push a value to the stack.
+   *
+   * @param value The value to store on the stack.
+   */
+  public void push(int value) {
+    if (start == null) {
+      start = new StackItem(value);
+    } else {
+      StackItem item = start;
+
+      // get the last item of the stack.
+      while (item.next != null) {
+        item = item.next;
+      }
+
+      // create a new stack item to store the value.
+      item.next = new StackItem(value);
+      item.next.prev = item;
+    }
+  }
+
+  /**
+   * Method to pop a value from the stack.
+   *
+   * @return The value from stack.
+   */
+  public int pop() {
+    StackItem item = start;
+
+    // get the last item of the stack.
+    while (item.next != null) {
+      item = item.next;
+    }
+
+    // remove last item from stack.
+    if (item.prev == null && item == start) {
+      start = null;
+    } else {
+      item.prev.next = null;
+    }
+
+    // return the value of the last item of the stack.
+    return item.value;
+  }
+}