1.5 - JDK, JRE, and JVM
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Introduction & Overview
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Quick Overview
Standard
This section elaborates on the roles of JDK (Java Development Kit), JRE (Java Runtime Environment), and JVM (Java Virtual Machine) in Java programming. The JDK includes tools for writing and compiling Java applications, the JRE offers a runtime environment for executing them, and the JVM interprets the compiled code to ensure platform independence.
Detailed
JDK, JRE, and JVM
In this section, we explore three foundational elements of Java programming:
-
JDK (Java Development Kit): The JDK is a software development kit that provides tools necessary for developing Java applications. It includes the JRE as well as additional development tools such as
javacfor compiling code andjavadocfor generating documentation. - JRE (Java Runtime Environment): The JRE is essential for running Java applications. It contains the JVM along with libraries that provide necessary functionalities for Java programs. The JRE allows developers to execute Java applications without the more complex tools included in the JDK.
- JVM (Java Virtual Machine): The JVM is the core component that acts as an interpreter between the compiled Java bytecode and the underlying operating system. It allows Java applications to run on different platforms without modification, enabling the languageβs famous slogan of
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Understanding JDK
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β JDK (Java Development Kit): A software development kit used to develop Java applications. It includes JRE + development tools like javac, javadoc, etc.
Detailed Explanation
The Java Development Kit (JDK) is essential for developing Java applications. It not only allows you to compile and run Java programs but also includes various development tools such as the Java compiler (javac), which translates your Java code into bytecode, and javadoc, a tool for generating documentation from Java source code. Essentially, if you're going to write Java programs, you'll need the JDK.
Examples & Analogies
Think of the JDK as a complete toolbox for a carpenter. Just as a carpenter needs different tools to build furniture, a Java developer needs the JDK's various tools to create software applications efficiently.
Understanding JRE
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β JRE (Java Runtime Environment): Provides an environment to run Java applications. It contains JVM + core libraries.
Detailed Explanation
The Java Runtime Environment (JRE) is a part of the Java ecosystem that provides the necessary environment for running Java applications. It includes the Java Virtual Machine (JVM) and core classes that your Java programs need to execute. Without the JRE, your Java applications wonβt run because the JRE ensures that the compiled bytecode is interpreted and executed correctly.
Examples & Analogies
Imagine the JRE as the stage where a play is performed. Just as the stage provides the necessary setting and equipment for actors (Java programs) to perform, the JRE provides the environment for your Java applications to run.
Understanding JVM
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β JVM (Java Virtual Machine): It interprets the compiled Java code (bytecode) and runs it on your machine. It makes Java platform-independent.
Detailed Explanation
The Java Virtual Machine (JVM) is a crucial component of the Java platform. It is responsible for interpreting the bytecode produced by the Java compiler and executing it. The JVM abstracts the underlying hardware, which means that Java applications can run on any device that has a JVM, regardless of the underlying operating system. This feature is what makes Java 'write once, run anywhere.'
Examples & Analogies
You can think of the JVM as a universal translator. Just like a translator converts one language into another so that people from different countries can understand each other, the JVM converts Java bytecode into machine code that the computerβs hardware can understand and execute.
Interrelationship Among JDK, JRE, and JVM
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Important: You write code using the JDK, and run code using the JRE/JVM.
Detailed Explanation
The JDK, JRE, and JVM work together in the Java programming environment. You start by writing your Java source code using tools found in the JDK. After writing your code, you compile it to create bytecode. To run this bytecode, you need the JRE, which contains the JVM that executes the bytecode. Therefore, understanding these components is vital for anyone wanting to develop in Java.
Examples & Analogies
Consider writing a book. You need a complete set of writing tools (the JDK) to write the book. Once written, you need a printing process (the JRE) to produce a physical copy. Finally, the printer (the JVM) takes your written text and turns it into a printed book that anyone can read. All three parts must work in harmony for your book (Java application) to exist and be shareable.