1.5 Exercises

1. A Simple Application

Create a file named hello.java with the flawed Java code shown here:

class Hi {
  public static void main (string[] args) {
    System.out.println("Hi "+ args[0])
  }
}

Adapt the source code so that it can be compiled without any difficulty.

See how the Java program executes when it is called in the following four ways:

java Hi everybody
java hello everybody
java Hi
java Hi Ana and Bob
java Hi "Ana and Bob"

2. Hello Applet

Write a Hello applet that welcomes the person(s) mentioned in a parameter in the Web page that includes your applet.
Write a Hello applet that welcomes the person(s) mentioned in a text field in the Web page that includes your applet.

3. A Button

One of the classes defined in the AWT package is Button. To create a new button, say with name b and with the text push me, use:

b = new Button("push me");

The method setLabel can be used to change the text on the button. For example, to change the text from push me into thank you use:

b.setLabel("thank you");

Use the last example of the echo applet to write a Java applet with a "push me" button, i.e., a button that changes its label from push me to thank you when pressed. It should look like:

4. Traffic Light (optional exercise)

Write a "Traffic Light" applet with a "switch color" button that looks like:

To work with the color red, yellow, and green, you have to know the following:

The Color class is of course for working with colors. The Color.red object is the red color, and for the other colors you have similar names.
Testing equality of colors can be done with the equals method. For example
```
Color c = Color.red;
c.equals(Color.yellow);
```
will test if the color c is yellow and will return false.
To set the background color of the applet, you use the setBackground method. For example,
```
setBackground(Color.red);
```
gives a red applet.