addded Bag-datastructure

data_structures/Bags/Bag.java

@@ -0,0 +1,126 @@
+package Bags;
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+/**
+ * Collection which does not allow removing elements (only collect and iterate)
+ * 
+ * @param <Element> - the generic type of an element in this bag
+ */
+public class Bag<Element> implements Iterable<Element> {
+
+	private Node<Element> firstElement; // first element of the bag
+	private int size; // size of bag
+
+	private static class Node<Element> {
+		private Element content;
+		private Node<Element> nextElement;
+	}
+
+	/**
+	 * Create an empty bag
+	 */
+	public Bag() {
+		firstElement = null;
+		size = 0;
+	}
+
+	/**
+	 * @return true if this bag is empty, false otherwise
+	 */
+	public boolean isEmpty() {
+		return firstElement == null;
+	}
+
+	/**
+	 * @return the number of elements
+	 */
+	public int size() {
+		return size;
+	}
+
+	/**
+	 * @param element - the element to add
+	 */
+	public void add(Element element) {
+		Node<Element> oldfirst = firstElement;
+		firstElement = new Node<>();
+		firstElement.content = element;
+		firstElement.nextElement = oldfirst;
+		size++;
+	}
+	
+	/**
+	 * Checks if the bag contains a specific element
+	 * 
+	 * @param element which you want to look for
+	 * @return true if bag contains element, otherwise false
+	 */
+	public boolean contains(Element element) {
+		Iterator<Element> iterator = this.iterator();
+		while(iterator.hasNext()) {
+			if (iterator.next().equals(element)) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	/**
+	 * @return an iterator that iterates over the elements in this bag in arbitrary order
+	 */
+	public Iterator<Element> iterator() {
+		return new ListIterator<>(firstElement);
+	}
+
+	@SuppressWarnings("hiding")
+	private class ListIterator<Element> implements Iterator<Element> {
+		private Node<Element> currentElement;
+
+		public ListIterator(Node<Element> firstElement) {
+			currentElement = firstElement;
+		}
+
+		public boolean hasNext() {
+			return currentElement != null;
+		}
+
+		/**
+		 * remove is not allowed in a bag
+		 */
+		@Override
+		public void remove() {
+			throw new UnsupportedOperationException();
+		}
+
+		public Element next() {
+			if (!hasNext())
+				throw new NoSuchElementException();
+			Element element = currentElement.content;
+			currentElement = currentElement.nextElement;
+			return element;
+		}
+	}
+
+	/**
+	 * main-method for testing
+	 */
+	public static void main(String[] args) {
+		Bag<String> bag = new Bag<>();
+
+		bag.add("1");
+		bag.add("1");
+		bag.add("2");
+
+		System.out.println("size of bag = " + bag.size());
+		for (String s : bag) {
+			System.out.println(s);
+		}
+		
+		System.out.println(bag.contains(null));
+		System.out.println(bag.contains("1"));
+		System.out.println(bag.contains("3"));
+	}
+
+}