Java Debugger (JDB)

Java Debugger (JDB) is a simple command-line tool provided by Java to help programmers find and fix bugs in their Java programs. It is a lightweight Java debugger that comes with the JDK.

It allows users to set breakpoints, inspect variables, step through the code line by line, and control the execution of Java applications. Even though it is a basic tool compared to graphical debuggers found in IDEs, JDB provides a strong understanding of how debugging works under the hood.

JDB Command Line Tool

JDB is a command-line debugger that comes bundled with the Java Development Kit (JDK). It is especially useful for debugging Java programs when a graphical interface is not available or necessary.

With JDB, developers can:

• Start a Java program and pause its execution at specific points (breakpoints).
• Step through the program one line at a time (step into, step over).
• Inspect and modify variables during program execution.
• View call stacks to understand the sequence of method calls.
• Evaluate expressions during runtime to see how different parts of the program behave.

JDB is started from the command line by typing jdb followed by the name of the class or application to debug. It connects either directly to a running JVM or starts the application in debug mode itself.

Debugging in IDE

While JDB is a command-line tool, modern Integrated Development Environments (IDEs) like Eclipse use similar underlying mechanisms to perform debugging tasks but provide a graphical user interface (GUI) on top of it. In Eclipse:

• Developers can easily set breakpoints by clicking beside the code lines.
• The IDE automatically uses a debugging protocol (similar to what JDB uses internally) to communicate with the Java Virtual Machine (JVM).
• When the program hits a breakpoint, Eclipse pauses execution and allows the developer to inspect variables, change their values, and control program flow using buttons like “Step Into”, “Step Over”, and “Continue”.
• Eclipse provides advanced features like conditional breakpoints, watchpoints (monitoring variable changes), and thread management, making debugging easier and more powerful than using the JDB command-line tool alone.
• Behind the scenes, Eclipse uses the Java Debug Interface (JDI), which is a higher-level API compared to JDB, but conceptually, it performs tasks similar to what a developer would manually do with JDB.

Using an IDE like Eclipse for debugging is much more beginner-friendly as it eliminates the need to remember command-line instructions and provides a visual, intuitive environment for troubleshooting and correcting code errors.