RunTime Class in Java

• The RunTime class in Java offers a wide range of capabilities that can greatly enhance the functionality and performance of Java applications. Let's dive into some of its key features and how they can be utilized effectively.

1. Executing System Commands

• The ability to run system commands from within a Java programme is one of the main functions of the RunTime class. With the help of this feature, developers can easily combine Java applications and the underlying operating system. By utilizing the exec() method provided by the RunTime class, developers can execute commands such as creating directories, launching external programs, or even performing complex system operations.

Java code demonstrates how to use the RunTime class to run the system command create new directory.

import java.io.IOException;

public class RuntimeExample {
    public static void main(String[] args) {
        try {
            // Create a new directory using the 'mkdir' command
            Process process = Runtime.getRuntime().exec("mkdir new_directory");

            // Wait for the process to complete
            process.waitFor();

            System.out.println("Directory created successfully!");
        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
        }
    }
}

Directory created successfully!
 

Developers can easily interact with the operating system and complete a variety of tasks by utilising the power of the RunTime class.

2. Managing Processes

• Another important feature of the RunTime class is its ability to manage processes. The exec() method returns an instance of the Process class, which represents a subprocess created by the Java application. This allows developers to monitor and control the execution of external programs from within their Java code.

Java code example where we execute a system command to launch an external program and wait for its completion.

import java.io.IOException;

public class RuntimeExample {
    public static void main(String[] args) {
        try {
            // Launch an external program using the 'notepad' command
            Process process = Runtime.getRuntime().exec("notepad");

            // Wait for the process to complete
            process.waitFor();

            System.out.println("External program executed successfully!");
        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
        }
    }
}

External program executed successfully!
 

In this example, the RunTime class is utilized to execute the "notepad" command, which launches the Notepad application. The waitFor() method ensures that the Java application waits until the external program completes its execution.

3. Retrieving Information about the Java Virtual Machine (JVM)

• The RunTime class provides methods to retrieve various information about the Java virtual machine (JVM). This includes information on the number of processors, Java version, and total memory made available to the JVM.

Java code snippet demonstrates how to use the RunTime class to retrieve the total memory available to the JVM

public class RuntimeExample {
    public static void main(String[] args) {
        // Get the Java runtime
        Runtime runtime = Runtime.getRuntime();

        // Get the total memory available to the JVM in bytes
        long totalMemory = runtime.totalMemory();

        System.out.println("Total memory: " + totalMemory + " bytes");
    }
}

 Total memory: [totalMemory value] bytes
 

Developers can learn more about the runtime environment and make wise decisions based on the resources available by utilising the methods provided by the RunTime class.

Methods of Java Runtime class

Example of the freeMemory() and totalMemory() methods of the Java Runtime

public class Main{
    public static void main(String arg[]) {
        //getRuntime()
        Runtime runtime = Runtime.getRuntime();
        System.out.println("Free Memory :" + runtime.freeMemory());
        
        // totalMemory()  
        System.out.println("Total Memory : "+runtime.totalMemory());  
        
        for(int i=0;i<1000;i++){  // Creating 1000 instance
        	new Main();  
        } 
        //freeMemory()
        System.out.println("Free Memory after creating 1000 instance : " + Runtime.getRuntime().freeMemory());
        System.gc(); 
        // The garbage collector is started. 
        //This method's name implies that the Java virtual machine makes 
        //greater efforts to recycle unused objects in order to make the 
        //memory they currently occupy available for quick reuse. 
        System.out.println("Free Memory after Running Garbage Collection : " 
                                                + Runtime.getRuntime().freeMemory());
   }
}

Free Memory :199312320
Total Memory : 201326592
Free Memory after creating 1000 instance : 199312320
Free Memory after Running Garbage Collection : 7672824 

Java Program to Demonstrate the Runtime class Using the exec() Method

public class Main{
    public static void main(String arg[]){
        // Creating a process and execute MS Word
        try {
			Process process = Runtime.getRuntime().exec("WINWORD"); // it will open ms word
		} catch (Exception  e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
        System.out.println("MS Word Open successfully");
    }
}

MS Word Open successfully 

Java program to demonstrate the Runtime class exit() Method, availableProcessors() Method

public class Main{
    public static void main(String arg[]){
        //availableProcessors() method
        System.out.println("" + Runtime.getRuntime().availableProcessors());
        
        //exit() method
        Runtime.getRuntime().exit(0); 
        System.out.println("Program Running Check");
    }
}

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Frequently Asked Questions (FAQ) - RunTime Class in Java