Java Runtime class

public class Runtime extends Object

The java.lang.Runtime class allows the application to interface with the environment in which the application is running.

It helps to us interact with java run-time environment. This class contains method to invoke Garbage Collector, free memory, total memory available or execute a process etc.

java.lang.Runtime class is a Singleton for a java application.

Some useful methods:

Method	Description
public static Runtime getRuntime()	Runtime is Singleton class. This method returns the instance of Runtime class.
public void exit(int status)	This method terminates the currently running Java virtual machine by initiating its shutdown sequence.
public void addShutdownHook(Thread hook)	Registers new hook thread.
public Process exec(String command)throws IOException	Executes given command in a separate process.
public int availableProcessors()	Returns the number of available processors.
public long freeMemory()	Returns amount of free memory in JVM.
public long totalMemory()	Returns amount of total memory in JVM.
boolean removeShutdownHook(Thread hook)	This method de-registers a previously-registered virtual-machine shutdown hook.

Open Command prompt using exec() method

import java.io.IOException;

public class Test {

     public static void main(String[] args) throws Exception {

           Runtime rt = Runtime.getRuntime();

           try {

                rt.exec(new String[]{"cmd.exe","/c","start"});

           } catch (IOException e) {

           }

     }

}

Memory test using Runtime class:

public class Test {

     public static void main(String args[]) { 

           Runtime runtime = Runtime.getRuntime(); 

           System.out.println("Total Memory:"+runtime.totalMemory()); 

           System.out.println("Free Memory: "+runtime.freeMemory()); 

           for(int i=0;i<Integer.MAX_VALUE;i++){ 

                Object object = new Object(); 

           }

          

           System.out.println("After creating instance of Object");

           System.out.println("Free Memory: "+runtime.freeMemory());

          

           System.out.println("After calling gc()");

           System.gc();

           System.out.println("Free Memory: "+runtime.freeMemory()); 

     } 

}

Output:

Total Memory:61800448

Free Memory: 61476688

After creating instance of Object

Free Memory: 60996792

After calling gc()

Free Memory: 61335224