Java HashTable is synchronized.
Iterator in the HashMap is fail-safe while the enumerator for the Hashtable isn’t.
Java Hashtable doesn’t allow nulls
Below is a HashTable Example showing how collections are manipulated using a HashTable
Please Note that It must be Compiled in Java 1.4.
// Demonstrates the Hashtable class of the java.util package. public class HashTableDemo extends JFrame { public HashTableDemo() { super(" Hashtable Sourcecode Example"); final JLabel jlbStatus = new JLabel(); final Hashtable hashTable = new Hashtable(); final JTextArea display = new JTextArea(4, 20); display.setEditable(false); JPanel jplNorth = new JPanel(); jplNorth.setLayout(new BorderLayout()); JPanel jplNorthSub = new JPanel(); jplNorthSub.add(new JLabel("Name (Key)")); final JTextField jtfFirstName = new JTextField(8); jplNorthSub.add(jtfFirstName); jplNorthSub.add(new JLabel("Phone No")); final JTextField jtfPhone = new JTextField(8); jplNorthSub.add(jtfPhone); jplNorth.add(jplNorthSub, BorderLayout.NORTH); jplNorth.add(jlbStatus, BorderLayout.SOUTH); JPanel jplSouth = new JPanel(); jplSouth.setLayout(new GridLayout(2, 5)); JButton jbnAdd = new JButton("Add"); jbnAdd.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { String strNum = jtfPhone.getText().trim(); String strName = jtfFirstName.getText().trim(); if ((strNum != null && strNum.equals("")) || (strName != null && strName.equals(""))) { JOptionPane.showMessageDialog(HashTableDemo.this, "Please enter both Name and Phone No"); return; } int num = 0; try { num = Integer.parseInt(strNum); } catch (NumberFormatException ne) { ne.printStackTrace(); } EmployeeDetails emp = new EmployeeDetails(strName, num); Object val = hashTable.put(strName, emp); if (val == null) jlbStatus.setText("Added: " + emp.toString()); else jlbStatus.setText("Added: " + emp.toString() + "; Replaced: " + val.toString()); } }); jplSouth.add(jbnAdd); JButton jbnGet = new JButton("Get"); jbnGet.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { Object val = hashTable.get(jtfFirstName.getText().trim()); if (val != null) jlbStatus.setText("Get: " + val.toString()); else jlbStatus.setText("Get: " + jtfFirstName.getText()+ " not in table"); } }); jplSouth.add(jbnGet); JButton jbnRemove = new JButton("Remove Name"); jbnRemove.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { Object val = hashTable.remove(jtfFirstName.getText() .trim()); if (val != null) jlbStatus.setText("Remove: " + val.toString()); else jlbStatus.setText("Remove: " + jtfFirstName.getText()+ " not in table"); } }); jplSouth.add(jbnRemove); JButton jbnIsEmpty = new JButton("Empty ?"); jbnIsEmpty.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { jlbStatus.setText("Empty: " + hashTable.isEmpty()); } }); jplSouth.add(jbnIsEmpty); JButton jbnContains = new JButton("Contains key"); jbnContains.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { jlbStatus.setText("Contains key: "+ hashTable.containsKey(jtfFirstName.getText().trim())); } }); jplSouth.add(jbnContains); JButton jbnClear = new JButton("Clear table"); jbnClear.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { hashTable.clear(); jlbStatus.setText("HashTable Emptied"); } }); jplSouth.add(jbnClear); JButton jbnDisplay = new JButton("List objects"); jbnDisplay.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { StringBuffer buf = new StringBuffer(); for (Enumeration enum = hashTable.elements(); enum.hasMoreElements();) buf.append(enum.nextElement()).append('\n'); display.setText(buf.toString()); } }); jplSouth.add(jbnDisplay); JButton jbnKeys = new JButton("List keys"); jbnKeys.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { StringBuffer buf = new StringBuffer(); for (Enumeration enum = hashTable.keys(); enum.hasMoreElements();) buf.append(enum.nextElement()).append('\n'); JOptionPane.showMessageDialog(null, buf.toString(), "Display Keys of HashTable ",JOptionPane.PLAIN_MESSAGE); } }); jplSouth.add(jbnKeys); Container c = getContentPane(); c.add(jplNorth, BorderLayout.NORTH); c.add(new JScrollPane(display), BorderLayout.CENTER); c.add(jplSouth, BorderLayout.SOUTH); setSize(540, 300); setVisible(true); } public static void main(String args[]) { HashTableDemo hashTableDemo = new HashTableDemo(); hashTableDemo.addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent e) { System.exit(0); } }); } } class EmployeeDetails { private String name; private int phoneNp; public EmployeeDetails(String fName, int phNo) { name = fName; phoneNp = phNo; } public String toString() { return name + " " + phoneNp; } }
Output
Download HashTableDemo.java