One long section of code outlining how to use the Java Collections. As per the Java Strings post, this consists of one long code snippet outlining commonly used Java collections such as Hash Maps, Linked Lists etc. As this is ongoing, expect to see newer stuff added as time progresses.
package javacollections; import java.util.*; public class JavaCollections { public static void main(String[] args) { // 1. Hash maps HashMap hm = new HashMap(); hm.put("Tinker", new Double(3434.34)); hm.put("Tailor", new Double(123.22)); hm.put("Soldier", new Double(123.22)); hm.put("Spy", new Double(123.22)); Double value = (Double) hm.get("Soldier"); // 123.22 // 2. HashSet: holds unique values only Set set = new HashSet(); set.add("XYZ"); set.add("ABC"); set.add("BCD"); set.add("ABC"); int size = set.size(); // 3 set.remove("ABC"); boolean contains = set.contains("ABC"); // false contains = set.contains("XYZ"); // true int number = set.size(); // 2 // Create array containing string elements in set String[] array = (String[]) set.toArray(new String[set.size()]); // Iterate over set elements Iterator it = set.iterator(); while (it.hasNext()) { Object element = it.next(); String str = (String) element; System.out.println( str ); } // 3. List - a doubly-linked list List list = new LinkedList(); // Doubly-linked list list.add("a"); // Append element to list list.add(0, "b"); // Insert element at head of list list.add(0, "b"); // Ditto list.add(0, "c"); // Ditto size = list.size(); // 3 Object element = list.get(list.size()-1); // "a" element = list.get(0); // "a" boolean b = list.remove("b"); // Remove 1st occurence - true b = list.remove("b"); // true list.remove( 0 ); // Remove element at index // 4. Map - type specific Map<Integer, String> map = new HashMap<Integer, String>(); map.put(1, "first"); map.put(21, "twenty first"); map.put(22, "twenty second"); String text = map.get(21); // "twenty first" // 5. Sorted Set SortedSet sset = new TreeSet(); sset.add("XYZ"); sset.add("BCD"); sset.add("ABC"); sset.add("CBA"); System.out.println(sset); // 6. Arraylist ArrayList al = new ArrayList(); al.add("C"); al.add("A"); al.add("E"); System.out.println(al); al.add(1, "A2"); System.out.println(al); System.out.println(al.toString()); // Dictionary / Vector considered obsolete // use HashMap / ArrayList respectively } }