- Supakon Khongkrajang
As a Java developer, mastering the command line tools is essential for efficient coding, debugging, and managing Java applications. In this guide, we will explore the basic use of the
java command and its associated tools that every Java developer should know.
1. Checking Your Java Version
Before you start any Java development work, it's crucial to confirm your Java installation's version:
This command displays information about the installed Java version. Ensuring the correct version is in place is the first step in avoiding compatibility issues.
2. Getting Help
Whenever you need a quick reference for the available options and usage of the
java command, use the
This command provides a concise summary of the available options, which can be invaluable for navigating the
java command's extensive capabilities.
3. Compiling Java Code with
To compile your Java source code into bytecode that the Java Virtual Machine (JVM) can execute, you'll need to use the
This command generates
.class files that are ready for execution.
4. Running Java Applications
Once your Java code is compiled, you can execute it using the
This command launches your Java application, and you should see the program's output in the console.
5. Passing Command-Line Arguments
Java applications often accept input from the command line. You can pass arguments to your Java program like this:
java YourMainClass arg1 arg2 arg3
These arguments can be accessed within your Java code through the
args array in the
6. Specifying the Classpath with
-classpath) option allows you to specify the classpath, which tells the JVM where to find classes and resources:
java -cp path/to/your/library.jar YourMainClass
This ensures that your application can access the necessary classes and resources.
7. Running Executable JARs with
Executable JAR files simplify the distribution of Java applications. Execute them using the
java -jar YourApp.jar
This command extracts the main class and other metadata from the JAR's manifest file.
8. Defining System Properties with
You can configure your Java application at runtime by specifying system properties:
java -Dmyapp.config=config.properties YourMainClass
This is useful for dynamically adjusting your application's behavior.
9. Memory Management with
Fine-tuning memory allocation is crucial for Java applications:
-Xmxsets the maximum heap size, e.g.,
-Xmssets the initial heap size, e.g.,
-Xssadjusts the thread stack size, e.g.,
These options are essential for optimizing memory usage, especially in memory-intensive applications.
10. Activating Assertions with
To catch and handle bugs early in the development process, activate assertions in your code with
java -ea YourMainClass
Assertions ensure that your code behaves as expected.
11. Enabling Verbose Output with
For in-depth debugging and performance analysis, enable verbose output for garbage collection with
java -verbose:g YourMainClass
This option provides detailed information about garbage collection activities.
12. Debugging with
For advanced debugging scenarios, enable Java Debug Wire Protocol (JDWP) with these options:
java -Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=5005 YourMainClass
This allows you to connect a debugger for comprehensive debugging sessions.
By mastering these basic uses of the
java command and its associated options, you'll be well-equipped to develop, test, and troubleshoot Java applications efficiently. As you progress in your Java development journey, you'll discover even more advanced capabilities of these essential tools. Happy coding!