How to find the Java major and minor versions from a .class file

Every Java release internally maintains a major and minor version numbers.

 

Below table summarizes different major.minor versions of Jdk.

 

JDK version	Major version number
JDK 1.1	45
JDK 1.2	46
JDK 1.3	47
JDK 1.4	48
Java SE 5.0	49
Java SE 6.0	50
Java SE 7	51
Java SE 8	52
Java SE 9	53
Java SE 10	54
Java SE 11	55
Java SE 12	56
Java SE 13	57
Java SE 14	58
Java SE 15	59
Java SE 16	60
Java SE 17	61

 

When you compile a Java class file, major and minor version numbers will be added to the Java class file. Using javap command, we can read this from .class file.

 

HelloWorld.java

public class HelloWorld {
	
	public static void main(String[] args) {
		System.out.println("Hello World");
	}

}

Compile HelloWorld.java file.

$javac HelloWorld.java 
$
$ls
HelloWorld.class	HelloWorld.java

Execute the command ‘javap -verbose HelloWorld.class’ to see the content of .class file.

$javap -verbose HelloWorld.class
Classfile /Users/krishna/Documents/technical-documents/examples/HelloWorld.class
  Last modified 17 May, 2022; size 425 bytes
  MD5 checksum 1e678fa12f97b65fdde287539d5ce419
  Compiled from "HelloWorld.java"
public class HelloWorld
  minor version: 0
  major version: 52
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Methodref          #6.#15         // java/lang/Object."<init>":()V
   #2 = Fieldref           #16.#17        // java/lang/System.out:Ljava/io/PrintStream;
   #3 = String             #18            // Hello World
   #4 = Methodref          #19.#20        // java/io/PrintStream.println:(Ljava/lang/String;)V
   #5 = Class              #21            // HelloWorld
   #6 = Class              #22            // java/lang/Object
   #7 = Utf8               <init>
   #8 = Utf8               ()V
   #9 = Utf8               Code
  #10 = Utf8               LineNumberTable
  #11 = Utf8               main
  #12 = Utf8               ([Ljava/lang/String;)V
  #13 = Utf8               SourceFile
  #14 = Utf8               HelloWorld.java
  #15 = NameAndType        #7:#8          // "<init>":()V
  #16 = Class              #23            // java/lang/System
  #17 = NameAndType        #24:#25        // out:Ljava/io/PrintStream;
  #18 = Utf8               Hello World
  #19 = Class              #26            // java/io/PrintStream
  #20 = NameAndType        #27:#28        // println:(Ljava/lang/String;)V
  #21 = Utf8               HelloWorld
  #22 = Utf8               java/lang/Object
  #23 = Utf8               java/lang/System
  #24 = Utf8               out
  #25 = Utf8               Ljava/io/PrintStream;
  #26 = Utf8               java/io/PrintStream
  #27 = Utf8               println
  #28 = Utf8               (Ljava/lang/String;)V
{
  public HelloWorld();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial #1                  // Method java/lang/Object."<init>":()V
         4: return
      LineNumberTable:
        line 1: 0

  public static void main(java.lang.String[]);
    descriptor: ([Ljava/lang/String;)V
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=2, locals=1, args_size=1
         0: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
         3: ldc           #3                  // String Hello World
         5: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
         8: return
      LineNumberTable:
        line 4: 0
        line 5: 8
}
SourceFile: "HelloWorld.java"

From the output, you can notice below lines.

 

  minor version: 0

  major version: 52

 

major version 52 refer Java SE 8, you can confirm the same from above table.

 

Since the output of javap command is verbose, you can grep for the major and minor versions using below commands.

Linux, Mac

javap -verbose HelloWorld.class | grep "major"

javap -verbose HelloWorld.class | grep "minor"

 

Windows

javap -verbose HelloWorld .class | findstr "major"

javap -verbose HelloWorld .class | findstr "minor"

$javap -verbose HelloWorld.class | grep "major"
  major version: 52
$
$
$javap -verbose HelloWorld.class | grep "minor"
  minor version: 0

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