Difference between JDK, JRE and JVM

Three names that look similar — JVM, JRE, JDK. Freshers mix them. Learn them as three boxes, one inside the other.

JVM (Java Virtual Machine) is the engine. It reads bytecode and runs your program. Without JVM, a .class file does nothing.

JRE (Java Runtime Environment) is JVM plus the libraries needed to run a ready app. If you only want to run a Java program, JRE is enough.

JDK (Java Development Kit) is JRE plus tools for writing code — mainly javac (compiler). If you write programs in college, you install JDK, not only JRE.

Picture — JDK contains JRE. JRE contains JVM. Developer → JDK. Only run apps → JRE. Engine inside → JVM.

Let's take this on the board with one tiny Main class — no extra files. Difference between JDK, JRE and JVM — output: JVM → runs bytecode / JRE → JVM + libraries / JDK → JRE + javac/tools. Say that nesting in the viva. Start from main, go line by line, and stop at each print. That output is the proof for Difference between JDK, JRE and JVM.

Diagram

JDK   (write + compile)
    javac + tools
      JRE   (run apps)
        libraries
          JVM   (run bytecode)

Exam tip

Draw JDK > JRE > JVM. One line each.

Example

// JDK / JRE / JVM — remember the nesting
public class Main {
  public static void main(String[] args) {
    System.out.println("JVM  → runs bytecode");
    System.out.println("JRE  → JVM + libraries");
    System.out.println("JDK  → JRE + javac/tools");
  }
}

Difference between JDK, JRE and JVM — output: JVM → runs bytecode / JRE → JVM + libraries / JDK → JRE + javac/tools. Say that nesting in the viva.

Short notes

DefJVM = engine that runs bytecode. JRE = run apps. JDK = write + compile.
RuleJDK contains JRE. JRE contains JVM.
RememberA student must install JDK, not only JRE (need javac).
DiffJDK ≠ JRE. One is for building, one is mainly for running.

Difference between JDK, JRE and JVM

Three names that look similar — JVM, JRE, JDK. Freshers mix them. Learn them as three boxes, one inside the other.

JVM (Java Virtual Machine) is the engine. It reads bytecode and runs your program. Without JVM, a .class file does nothing.

JRE (Java Runtime Environment) is JVM plus the libraries needed to run a ready app. If you only want to run a Java program, JRE is enough.

JDK (Java Development Kit) is JRE plus tools for writing code — mainly javac (compiler). If you write programs in college, you install JDK, not only JRE.

Picture — JDK contains JRE. JRE contains JVM. Developer → JDK. Only run apps → JRE. Engine inside → JVM.

Diagram

JDK   (write + compile)
    javac + tools
      JRE   (run apps)
        libraries
          JVM   (run bytecode)

Exam tip

Draw JDK > JRE > JVM. One line each.

Example

// JDK / JRE / JVM — remember the nesting
public class Main {
  public static void main(String[] args) {
    System.out.println("JVM  → runs bytecode");
    System.out.println("JRE  → JVM + libraries");
    System.out.println("JDK  → JRE + javac/tools");
  }
}

Difference between JDK, JRE and JVM — output: JVM → runs bytecode / JRE → JVM + libraries / JDK → JRE + javac/tools. Say that nesting in the viva.

Short notes

DefJVM = engine that runs bytecode. JRE = run apps. JDK = write + compile.
RuleJDK contains JRE. JRE contains JVM.
RememberA student must install JDK, not only JRE (need javac).
DiffJDK ≠ JRE. One is for building, one is mainly for running.

Difference between JDK, JRE and JVM

Example

Short notes

Questions

Difference between JDK, JRE and JVM

Example

Short notes

Questions