Review

Import

• Understand the meaning of import
• Import by wild character , example import java.awt.*.
• Import by full name, example import javax.swing.JFrame.
• Import statements are not necessary. Example
  javax.swing.JFrame f = new javax.swing.JFrame("title").

Graphics

• know how to extend JFrame and override paint(Graphics g) method
• understand Font class and Color class, how to set/get font and color
• how to use drawLine, drawRect, fillRect, drawOval, fillOval, drawString methods

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

Interface

• know how to create an interface
• all member methods in an interface are public abstract
• all member variables in an interface are public static final
• know how to implement an interface

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
      } .....
        .....
  

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 occur.
• 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");
      }
  }
  

• Lazy way of taking care the exceptions

  public static void main(String[] args) throws Exception {
     // your codes
  }
  

  or

  public static void main(String[] args)  {
       try {
            // your codes
           
        } catch (Exception ex) {
           // catch all exception because all exception class are subclass of Exception
        }
  }
  

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.

Split

• String[] split(String exp) splits a String by exp. Example String s = "123ab456abXXX", then s.split("ab") returns {"123", "456", "XXX"}

Math

• understand how to use Math class. Example Math.sqrt(5) is used to calculate the square root of 5.
• Math.random() generates a random double between 0 and 0.99999999. To generate an integer random number from 0 to max-1, use (int)(max*Math.random()).