To test that your Java Development Kit (JDK) is installed correctly, you need to write a simple Java program, compile it, and run the compiled bytecode.
[andy@home-pc ~]$ mkdir ~/java-demos [andy@home-pc ~]$ cd ~/java-demos [andy@home-pc java-demos]$ vim HelloWorld.java
A simple Java HelloWorld example looks like this.
class HelloWorld {
public static void main(String[] args) {
System.out.println("\nThe Java Development Kit (JDK) is installed and working!!\n");
}
}
You compile Java code with the javac command, and then run the resulting file with the java command.
$ ls HelloWorld.java $ javac HelloWorld.java $ ls HelloWorld.class HelloWorld.java $ java HelloWorld The Java Development Kit (JDK) is installed and working!! $
You should note that although the resulting Java bytecode is a file called HelloWorld.class, you run the program without any file extension.
You could take this a step further and write some code that returns some Java system properties about the current installation.
$ ls HelloWorld.class HelloWorld.java $ cp -v HelloWorld.java JDKInstallationTest.java
The below code makes use of the getProperties() method, of the System</code class.
import java.util.Map;
class JDKInstallationTest {
public static void main(String[] args) {
System.out.println("\nThe " + System.getProperty("java.vendor") + " Java version " + System.getProperty("java.version") + " is installed on this system.\n");
// Print a list of Java properties
System.out.println("Java Properties:");
for(Map.Entry e : System.getProperties().entrySet()) {
if (((String)e.getKey()).startsWith("java")) {
System.out.println(e);
}
}
System.out.println();
}
}
Again, run it like so.
$ ls HelloWorld.class HelloWorld.java JDKInstallationTest.java $ javac JDKInstallationTest.java $ ls HelloWorld.class HelloWorld.java JDKInstallationTest.class JDKInstallationTest.java $ java JDKInstallationTest
The output will look something like this.
The Oracle Corporation Java version 1.8.0_31 is installed on this system. Java Properties: java.runtime.name=Java(TM) SE Runtime Environment java.vm.version=25.31-b07 java.vm.vendor=Oracle Corporation java.vendor.url=http://java.oracle.com/ java.vm.name=Java HotSpot(TM) 64-Bit Server VM java.vm.specification.name=Java Virtual Machine Specification java.runtime.version=1.8.0_31-b13 java.awt.graphicsenv=sun.awt.X11GraphicsEnvironment java.endorsed.dirs=/usr/lib/jvm/java-8-jdk/jre/lib/endorsed java.io.tmpdir=/tmp java.vm.specification.vendor=Oracle Corporation java.library.path=/usr/java/packages/lib/amd64:/usr/lib64:/lib64:/lib:/usr/lib java.specification.name=Java Platform API Specification java.class.version=52.0 java.awt.printerjob=sun.print.PSPrinterJob java.specification.version=1.8 java.class.path=. java.vm.specification.version=1.8 java.home=/usr/lib/jvm/java-8-jdk/jre java.specification.vendor=Oracle Corporation java.vm.info=mixed mode java.version=1.8.0_31 java.ext.dirs=/usr/lib/jvm/java-8-jdk/jre/lib/ext:/usr/java/packages/lib/ext java.vendor=Oracle Corporation java.vendor.url.bug=http://bugreport.sun.com/bugreport/ $
You can then delete the .class files if you wish, leaving only the source (.java) files.
$ ls HelloWorld.class HelloWorld.java JDKInstallationTest.class JDKInstallationTest.java $ rm -v ./*.class removed ‘./HelloWorld.class’ removed ‘./JDKInstallationTest.class’ $ ls HelloWorld.java JDKInstallationTest.java $
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