Java.lang.System.setProperty() Method



The java.lang.System.setProperty() method sets the system property indicated by the specified key.


Following is the declaration for java.lang.System.setProperty() method

public static String setProperty(String key, String value)


  • key − This is the name of the system property.

  • value − This is the value of the system property.

Return Value

This method returns the previous value of the system property, or null if it did not have one.


  • SecurityException − if a security manager exists and its checkPermission method doesn't allow setting of the specified property.

  • NullPointerException − if key or value is null.

  • IllegalArgumentException − if key is empty.


The following example shows the usage of java.lang.System.setProperty() method.

package com.tutorialspoint;

import java.lang.*;

public class SystemDemo {

   public static void main(String[] args) {

      // prints Java Runtime Version before property set
      System.out.print("Previous : ");
      System.out.println(System.getProperty("java.runtime.version" ));
      System.setProperty("java.runtime.version", "Java Runtime 1.6.0");
      // prints Java Runtime Version after property set
      System.out.print("New : ");
      System.out.println(System.getProperty("java.runtime.version" ));

Let us compile and run the above program, this will produce the following result −

Previous : 1.8.0_65-b17
New : Java Runtime 1.6.0