Review

JFrame

• getContentPane()
• how to set layout
• constructors
• setSize, setVisible, setLocation....

Layout

• 3 layouts: BorderLayout, FlowLayout, GridLayout
• the effect of different layout (how they look?)
• understand all the constructors
• What do new GridLayout(0, 5), new GridLayout(5,0) mean?
• add(component), remove(index), add(component, index)

JPanel

• use as an intermediate container for creating complicated Swing applications
• JPanel(), JPanel(layout)

JLabel, JButton, JTextField

• constructors
• getText, setText
• setBackground
• know how to set text position, icons, etc etc
• getActionCommand, setActionCommand

ActionListener

• public class XXX implements ActionListener {
      .............
      ............
      public void actionPerformed(ActionEvent e) {
          // your codes
      }
  }
  

• Anonymous class:

  button.addActionListener(new ActionListener() {
          public void actionPerformed(ActionEvent e) {
              // your codes
          }
      });
  

• familiar with them and know how to change form one form to another

ActionEvent

e.getSource()

• returns Component
• may need to downcast it, example:
  

  JButton button = (JButton)e.getSource();
  

• can be used to distinguish sources of the event, example
  

  public void actionPerformed(ActionEvent e) {
      if(e.getSource() == button1) {
           // do something
       } else if( e.getSource() == button2) {
          // do something
      } ......
        .....
  }
  

e.getActionCommand()

• returns the actionCommand(as a String) of the source
• e.g. button.setActionCommand(String s) set the action command of the button to s. If you don't set it, the default value is the text on the button.
• can be used to distinguish sources of the event, example
  

  public void actionPerformed(ActionEvent e) {
       String action = e.getActionCommand();
       if(action.equals(string1)) {
          // do something
       } else if (action.equals(string2)) {
           // do something
      } .....
        .....
  

Applet

• how to write html file that includes an applet

• MyApplet extends Applet {
       public void init() {
           ........
       }
  }
  

  replace constructor by init
• how to run an applet
• how to deal with parameter?
  • <param name="somename" value="somevalue">
  • String getParameter(somename) return the value (as a String)
• works like a JPanel or JFrame. You can setLayout, or add(component)

Exception

• There are 2 types of exception: RuntimeException, Checked exception
• RuntimeExceptions are classes that extends RuntimeException.
• You have to "take care" of checked exception. There will be compiler error if you don't do that.
  2 ways of taking care of exceptions

  someMethod(......)  throws SomeException {
     // your code
  }
  

  or

  try {
      // some codes
  } catch (ExceptionX ex) {
       // some codes
  } catch (ExceptionY ex) {
      // some codes
  }
  .....
  

• It is optional to "take care" of the RuntimeException.
• NullPointerException, ArraryIndexOutOfBoundsException, ArithmeticException, NumberFormatException are all RuntimeExceptions. Understand when will these exceptions occur.
• FileNotFoundException, IOException are checked exceptions. You should know when these exceptions occurs.
• You should understand the flow of the program with exception: example

  try {
     line1
     line2
     line3
     ......
     line10
  } catch (ExceptionX ex) {
     lineX
     ......
  } catch (ExceptionY ex) {
     lineY
     .......
     
  } finally {
      ......
  } 
  line101
  line102
  
  

  If the first exception occurs at line3, then the program will find out which exception matches the exceptin thrown by line 3. The codes in the catch block will be executed. After that, the codes in finally block will be executed. And then line 101.......
  Please modify the following program to understand the concept

  public class ExceptionTest {
      public static void main(String[] args) {
          try {
              System.out.println("line 1");
              String[] s = new String[10];
              
              System.out.println("line 2");
              s[0] = "Hi";
          
              System.out.println("line 3");
              System.out.println(s[11]);
          
              System.out.println("line 4");
              System.out.println(s[1].toUpperCase());
          
              System.out.println("line 5");
              System.out.println(10/0);
         } catch (ArrayIndexOutOfBoundsException ex) {
             System.out.println("line X");
         } catch (NullPointerException ex) {
             System.out.println("line Y");
         } catch (ArithmeticException ex) {
             System.out.println("line Z");
         } finally {
             System.out.println("line finally");
         }
         System.out.println("Start all over");
      }
  }
  

Object

• equals (vs ==) and how to write equals method.
• toString (System.out.println(obj))
• instanceof: obj instanceof aClassName returns true if obj is of type aClassName. Returns false otherwise.
• every class extends Object

Type Wrapper class

• how to "convert" one type to another, example

  Double x = new Double(1.23);
  double = x.doubleValue();
  

• useful methods, eg. Double.parseDouble() or Double.MAX_VALUE
• There are lot of useful methods in Character class. Example, Character.isUpperCase(char ch), Character.isLetter(char ch)
• Why do we need them?

IO

Input

• InputStream
  • FileInputStream in = new FileInputStream(filename)
  • int read()

    int ch = -1;
    while((ch = in.read())!= -1) {
        // do something
    }
    

• BufferedReader:
  • BufferedReader in = new BufferedReader(new FileReader(filename));: create a BufferedReader from a file.
  • new BufferedReader(new InputStreamReader(System.in));: create a BufferedReader from user input
  • String readLine:

    String line = null;
    while((line = in.readLine())!=null) {
       // do something
    }
    

Output

• FileOutputStream
  • FileOutputStream out = new FileOutputStream(filename);
  • out.write(int ch)
• PrintStream
  • PrintStream out = new PrintStream(new FileOutputStream(filename));
  • out.print(...), out.println(....)
  • System.out is a PrintStream

• Most of the methods throw IOException or FileNotFoundException
• don't forget to close the stream by close()
• understand other read, write methods.

File

• understand all the constructors and methods
• create a File object doesn't mean the file is created!
• read the API. Try my sample exam.

StringTokenizer

• use to break a String into "tokens"
• Constructor: new StringTokenizer(String).
• String nextToken(), int countTokens(), boolean hasMoreTokens()

String s = "this is a string"
StringTokenizer st = new StringTokenizer(s);
while(st.hasMoreTokens()){
    System.out.println(st.nextToken());
}

this
is
a
string

String s = "12  35";
StringTokenizer st = new StringTokenizer(s);
int sum = Integer.parseInt(st.nextToken()) + Integer.parseInt(st.nextToken());

Vector/LinkedList

• understand all the constructors and API
• add(Object obj), get(int index), set(int index, Object obj, size(), remove(int index), remove(Object obj)
• boolean contains(Object obj),int indexOf(Object obj) : these methods use equals method to test equality
• Type casting: (String)vector.get(5) get method returns Object.
• primitive type: vector.add(new Integer(101)); you can' t add primitive type to a vector. instead, you have to use type wrapper class.
• get primitive type: ((Integer)vector.get(2)).intValue() returns int

Math

• understand how to use Math class. Example Math.sqrt(5) is used to calculate the square root of 5.