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What is difference between hash mapping and hash table?
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Answer / khalid
Both provide key-value access to data. The Hashtable is one
of the original collection classes in Java. HashMap is part
of the new Collections Framework, added with Java 2, v1.2.
The key difference between the two is that access to the
Hashtable is synchronized on the table while access to the
HashMap isn't. You can add it, but it isn't there by
default.
Another difference is that iterator in the HashMap is fail-
safe while the enumerator for the Hashtable isn't. If you
change the map while iterating, you'll know.
And, a third difference is that HashMap permits null values
in it, while Hashtable doesn't.
For new code, I would tend to always use HashMap.
| Is This Answer Correct ? | 11 Yes | 1 No |
Answer / murali.s
hashtable is a Synchronized.
hashmap is not a Synchrobnized.
Hashtable doesn,t accept null key,values
Hashmap accept null key,values
| Is This Answer Correct ? | 4 Yes | 0 No |
Answer / sandya
Yes... I agree with u khalid.
can u send the examples in CFW.
Thanks in Advance.
| Is This Answer Correct ? | 0 Yes | 1 No |
Answer / khalid
Both provide key-value access to data. The Hashtable is one
of the original collection classes in Java. HashMap is part
of the new Collections Framework, added with Java 2, v1.2.
The key difference between the two is that access to the
Hashtable is synchronized on the table while access to the
HashMap isn't. You can add it, but it isn't there by
default.
Another difference is that iterator in the HashMap is fail-
safe while the enumerator for the Hashtable isn't. If you
change the map while iterating, you'll know.
And, a third difference is that HashMap permits null values
in it, while Hashtable doesn't.
For new code, I would tend to always use HashMap.
| Is This Answer Correct ? | 0 Yes | 5 No |
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Question 5 [15] Consider the following classes, illustrating the Strategy design pattern: import java.awt.*; abstract class Text { protected TextApplet tA; protected Text(TextApplet tApplet) { tA = tApplet; } abstract public void draw(Graphics g); } class PlainText extends Text { protected PlainText(TextApplet tApplet) { super(tApplet); } public void draw(Graphics g) { g.setColor(tA.getColor()); g.setFont(new Font("Sans-serif", Font.PLAIN, 12)); g.drawString(tA.getText(), 20, 20); } } class CodeText extends Text { protected CodeText(TextApplet tApplet) { super(tApplet); } public void draw(Graphics g) { g.setColor(tA.getColor()); g.setFont(new Font("Monospaced", Font.PLAIN, 12)); g.drawString(tA.getText(), 20, 20); } } public class TextApplet extends java.applet.Applet { protected Text text; protected String textVal; protected Color color; public String getText() { return textVal; } public Color getColor() { return color; } public void init() { textVal = getParameter("text"); String textStyle = getParameter("style"); String textColor = getParameter("color"); if (textStyle == "code") text = new CodeText(this); else text = new PlainText(this); if (textColor == "red") color = Color.RED; else if (textColor == "blue") color = Color.BLUE; else color = Color.BLACK; } public void paint(Graphics g) { text.draw(g); 10 } } The Text class is more complicated than it should be (there is too much coupling between the Text and TextApplet classes). By getting rid of the reference to a TextApplet object in the Text class and setting the colour in the paint() method, one could turn the Text class into an interface and simplify the strategy classes considerably. 5.1 Rewrite the Text and PlainText classes to do what is described above. (6) 5.2 Explain the consequent changes that are necessary to the TextApplet class. (4) 5.3 Write an additional strategy class called FancyText (to go with your simplified strategy classes) to allow fancy text to be displayed for the value "fancy" provided for the style parameter. It should use the font Font ("Serif", Font.ITALIC, 12). (3) 5.4 Explain what changes are necessary to the TextApplet class for this. (2)
Core Java 
