Question

Fill in the blanks in each of the following sentences about the Java environment: a) The \(\quad\) command from the JDK executes a Java application. b) The \(\quad\) command from the JDK compiles a Java program. c) A Java source code file must end with the __ file extension. d) When a Java program is compiled, the file produced by the compiler ends with the __ file extension. e) The file produced by the Java compiler contains __ that are executed by the Java Virtual Machine.

Short answer

a) 'java', b) 'javac', c) '.java', d) '.class', e) bytecode

Step-by-step solution

- Identifying the Java Execution Command

To execute a Java application, the JDK provides a command specifically designed to launch Java programs. This command is called 'java'. It is used to start the Java Virtual Machine (JVM), which in turn runs the compiled Java bytecode.

- Identifying the Java Compilation Command

The process of compiling a Java program, which translates Java source code into bytecode that can be executed by the JVM, is done using the 'javac' command. The 'javac' command stands for Java compiler and it is part of the JDK.

- Recognizing Java Source File Extension

Java source code files are written in plain text and need to be saved with a specific file extension for the Java compiler to recognize and compile them. The required file extension for Java source code files is '.java'.

- Determining Compiled Java File Extension

After a Java program is compiled by the 'javac' command, it is transformed into bytecode. The files containing Java bytecode have a distinct file extension which is '.class'.

- Understanding the Content of Compiled Java Files

The files produced by the Java compiler contain bytecode, which is a low-level set of instructions that can be executed by the Java Virtual Machine (JVM). This bytecode is what allows Java to be a platform-independent language.

Key concepts

java command

The java command is a crucial part of the JDK that allows users to run Java applications. This command initiates the Java Virtual Machine (JVM), which is the environment where Java bytecode gets executed. When you use the java command, it looks for the Java application's main method, which serves as the entry point of the application.

For example, after compiling a Java program called MyApp, you would type java MyApp in the command line to execute it. During this process, the JVM interprets the compiled bytecode into machine language appropriate for the underlying hardware, allowing the program to run.

javac command

The javac command, standing for Java compiler, is an essential tool within the JDK for transforming Java source code into Java bytecode. The command takes .java files as input and produces .class files, which contain the compiled bytecode.

For instance, to compile a file called MyProgram.java, a user would navigate to the directory containing the file and type javac MyProgram.java into the command line. The javac command then checks the source code for errors and, if none are found, creates a MyProgram.class file with the Java bytecode.

Java source file extension

Every Java source file has a .java file extension, which signifies to the compiler that it contains Java source code. The naming convention is critical because the javac compiler expects files to end with this extension in order to process them.

When writing Java source code in a text editor, users must save their work with a .java extension, such as Calculator.java. This extension helps organize and recognize Java files within a project and ensures that the javac command can successfully compile the source code to bytecode.

Java compiled file extension

Once Java source code is compiled, it is saved as a .class file, which is the extension for compiled Java files. These .class files contain the Java bytecode that the Java Virtual Machine (JVM) can understand and execute.

Each .class file corresponds to a single Java class. For example, if you compile a source file named Student.java, the javac compiler will output a file named Student.class containing the bytecode. It is this .class file that you run when you use the java command.

Java bytecode

At the heart of Java's write-once-run-anywhere principle lies Java bytecode, which is a set of instructions that the Java Virtual Machine (JVM) can execute. Bytecode is the product of compiling Java source code, and it's what makes Java portable across different platforms.

Java bytecode is contained within .class files and is a low-level, optimized set of instructions that resemble assembly language. This design allows the JVM to quickly interpret and run Java programs on any device with a compatible JVM, without needing to recompile the source code for each specific machine architecture.