Java Data Structure

The class and interface of the structure

Enumeration ( Interface )

  Enumeration is widely used in data structure.The enumeration interface defines a way to retrieve consecutive elements from the data structure.This traditional interface has been replaced by an iterator,although rarely used,but it has not been abandoned.

import java.util.Vector;
        import java.util.Enumeration;
        public class EnumerationTester {
           public static void main(String args[]) {
              Enumeration<String> days;
              Vector<String> dayNames = new Vector<String>();
              dayNames.add("Sunday");
              dayNames.add("Monday");
              dayNames.add("Tuesday");
              dayNames.add("Wednesday");
              dayNames.add("Thursday");
              dayNames.add("Friday");
              dayNames.add("Saturday");
              days = dayNames.elements();
              while (days.hasMoreElements()){
                 System.out.println(days.nextElement()); 
              }
           }
        }

BitSet

  A BitSet class creates a special type of array to hold bit values,BitSet array size will increase with the need.

import java.util.BitSet;
 
public class BitSetDemo {
 
  public static void main(String args[]) {
     BitSet bits1 = new BitSet(16);
     BitSet bits2 = new BitSet(16);
      
     // set some bits
     for(int i=0; i<16; i++) {
        if((i%2) == 0) bits1.set(i);
        if((i%5) != 0) bits2.set(i);
     }
     System.out.println("Initial pattern in bits1: ");
     System.out.println(bits1);
     System.out.println("\nInitial pattern in bits2: ");
     System.out.println(bits2);
 
     // AND bits
     bits2.and(bits1);
     System.out.println("\nbits2 AND bits1: ");
     System.out.println(bits2);
 
     // OR bits
     bits2.or(bits1);
     System.out.println("\nbits2 OR bits1: ");
     System.out.println(bits2);
 
     // XOR bits
     bits2.xor(bits1);
     System.out.println("\nbits2 XOR bits1: ");
     System.out.println(bits2);
  }
}

Vector

  The size of a Vector can be dynamically changed as needed.So when creating an object do not have to specify the size of it.The Vector class implements a dynamic array,and ArrayList and similar,but two are different.

• Vector is accessed synchronously
• Vector contains many traditional methods,these methods do not belong to the collection framework

  Vector class supports four kinds of construction method.

1.Create a default vector,the default size is ten

Vector()

2.Create a vector of the specified size

Vector(int size)

3.Create a vector of the specified size,and specify the increment.Increments represent the number of elements each time the vector is incremented

Vector(int size,int incr)

4.Create a vector that contains the elements of the set

Vector(Collection c)

Stack

  Stack implements a back-in-first-out data structure.You can understand a stack as a vertically-distributed stack of objects, and when you add a new one, you place the new one at the top of the other.Stack is a subclass of Vector.

import java.util.*;
 
public class StackDemo {
 
    // push elements into the top of the stack
    static void showPush(Stack<Integer> st, int a) {
        st.push(new Integer(a));
        System.out.println("push(" + a + ")");
        System.out.println("stack: " + st);
    }
 
    // remove the object at the top of the stack
    static void showPop(Stack<Integer> st) {
        System.out.print("pop -> ");
        Integer a = (Integer) st.pop();
        System.out.println(a);
        System.out.println("stack: " + st);
    }
 
    public static void main(String args[]) {
        Stack<Integer> st = new Stack<Integer>();
        System.out.println("stack: " + st);
        showpush(st, 42);
        showpush(st, 66);
        showpush(st, 99);
        showpop(st);
        showpop(st);
        showpop(st);
        try {
            showpop(st);
        } catch (EmptyStackException e) {
            System.out.println("empty stack");
        }
    }
}

HashTable

  The HashTable class provides a means of organizing data based on user-defined key ( Hash key ) structures.The key is hashed, and the resulting hash code is used as an index for the values ​​stored in the table.

import java.util.*;

public class HashTableDemo {

   public static void main(String args[]) {
      // create a hash map
      Hashtable balance = new Hashtable();
      Enumeration names;
      String str;
      double bal;
      
      // specified the key and value
      balance.put("key1", new Double(3434.34));
      balance.put("key2", new Double(123.22));
      balance.put("key3", new Double(1378.00));
      balance.put("key4", new Double(99.22));
      balance.put("key5", new Double(-19.08));

      // show all balances in hash table.
      names = balance.keys();
      while(names.hasMoreElements()) {
         str = (String) names.nextElement();
         System.out.println(str + ": " +
         // get the value from this key
         balance.get(str));
      }
      System.out.println();
      // deposit 1,000 into key1`s account
      bal = ((Double)balance.get("key1")).doubleValue();
      balance.put("key1", new Double(bal+1000));
      System.out.println("key1's new balance: " +
      balance.get("key1"));
   }
}

Properties

  Properties inherit from the HashTable.Properties class represents a durable set of properties.Each key in the property list and its corresponding value is a string.

import java.util.*;

public class PropDemo {

   public static void main(String args[]) {
      // create
      Properties capitals = new Properties();
      Set states;
      String str;
      
      // put elements
      capitals.put("Illinois", "Springfield");
      capitals.put("Missouri", "Jefferson City");
      capitals.put("Washington", "Olympia");
      capitals.put("California", "Sacramento");
      capitals.put("Indiana", "Indianapolis");

      // get set-view of keys
      states = capitals.keySet(); 
      Iterator itr = states.iterator();
      while(itr.hasNext()) {
         str = (String) itr.next();
         System.out.println("The capital of " +
            str + " is " + capitals.getProperty(str) + ".");
      }
      System.out.println();

      // look for state not in list -- specify default
      str = capitals.getProperty("Florida", "Not Found");
      System.out.println("The capital of Florida is "
          + str + ".");
   }
}