Eclipse Tutorial

        Step 1: Starting Eclipse (on CS Linux machines)

The first screen that comes up after opening Eclipse is the Workspace Launcher. This screen allows you to choose where the projects you create will be saved. You may use the default, or specify a different location.

        Step 2: Choosing a Perspective

Step 3: Creating a New Java Project

Step 4: Creating a Program in the Project

Note: As you type, the code completion assistance may automatically come up to give you suggestions for completing the code. For instance, when you type a dot (.) after System and pause for a second, Eclipse displays a pop up menu with suggestions to complete the code, as shown below. You can then select the appropriate item from the menu to complete the code.

Step 5: Compiling and Running a Program

Step 6: Compile and Run Java Applications from the Command Line

1. Type cd workspace/myprograms to change the directory to workspace/myprograms.
2. Type java Welcome to run the program. A sample run of the output looks like the following:

   % java Welcome
   Welcome to Java
   

3. You may also compile the program using the javac command at the prompt:

   % javac Welcome.java
   

Step 7: Importing Existing Resources

Step 8: Debugging in Eclipse

To demonstrate debugging, let us use example that displays the current time. The source code for ShowCurrentTime.java can be obtained from here.
You may either import the file ShowCurrentTime.java or create a new class named ShowCurrentTime and type in the code yourself.

8.1 Setting breakpoints

You can execute a program line by line to trace it, but this is time-consuming if you are debugging a large program. Often, you know that some parts of the program work fine. It makes no sense to trace these parts when you only need to trace the lines of code that are likely to have bugs. In cases of this kind, you can use breakpoints.

A breakpoint is a stop sign placed on a line of source code that tells the debugger to pause when this line is encountered. The debugger executes every line until it encounters a breakpoint, so you can trace the part of the program at the breakpoint. Using the breakpoint, you can quickly move over the sections you know work correctly and concentrate on the sections causing problems.

There are several ways to set a breakpoint on a line. One way is to click on the line on which you want to put a breakpoint and then choose Run, Toggle Line Breakpoint from the main menu. You will see the line highlighted, and a breakpoint mark on the left of the line:

As you debug your program, you can set as many breakpoints as you want, and can remove breakpoints at any time during debugging. The project retains the breakpoints you have set when you exit the project. The breakpoints are restored when you reopen it.

8.2 Starting the Debugger

There are several ways to start the debugger. A simple way is shown below:

1. Set a breakpoint at the first statement in the main method in the Source Editor.
2. Click on ShowCurrentTime.java . Choose Run, Debug As, Java Application from the main menu to start debugging. You will first see the Confirm Perspective Switch dialog, as shown below:

   

   Click Yes to switch to the Debug perspective.

The program pauses at the first line in the main method. This line, called the current execution point, is highlighted in green. The current execution point marks the nest line of source code to be executed by the debugger.

When the program pauses at the execution point, you can issue debugging commands to control the execution of the program. You can also inspect or modify the values of variables in the program.

When Eclipse is in the debugging mode, the following toolbar buttons for debugging are displayed in the Debug window, as shown below. The toolbar button commands also appear in the Run menu:

• Resume resumes the execution of a paused program.
• Suspend temporarily stops execution of a program.
• Terminate ends the current debugging session.
• Step Into executes a single statement or steps into a method.
• Step Over executes a single statement. If the statement contains a call to a method, the entire method is executed without stepping through it.
• Step Return executes all the statements in the current method and returns to its caller.
• Run to Line runs the program, starting from the current execution point, and pauses and places the execution point on the line of code containing the cursor, or at a breakpoint.

Among the most powerful features of an integrated debugger is its capability to examine the values of variables, array items, and objects, or the values of the parameters passed in a method call. You can also modify a variable value if you want to try a new value to continue debugging without restarting the program.

To demonstrate it, choose Run, Step Over to execute one line in the source code, and you will see the value for totalMilliseconds in the Variables pane, as shown below:

The debugger is an indispensable, powerful tool that boosts your productivity. It may take you some time to become familiar with it, but the effort will pay off in the long run.

After finishing debugging, you may switch to the Java perspective by choosing Window, Open Perspective, Java from the main menu.

Step 9: Creating and Testing Java Applets

To run an applet, choose Run, Run As, Java Applet from the main menu. Eclipse automatically creates an HTML file to contain the applet and invokes the appletviewer utility to run the applet, as shown below.

public static int maxOf2(int a, int b) throws AssertionError
{
	int answer = 1;
	if (a>b) answer = a;
	else answer =b;
		
	assert((answer==a)||(answer==b)): "maxOf2 answer is not equal to one of the arguments";
		
	return answer;
}