Java System setProperty() Method

The System.setProperty() method in Java is used to set the value of a system property.

Table of Contents

  1. Introduction
  2. setProperty() Method Syntax
  3. Examples
    • Basic Usage
    • Modifying Existing Properties
    • Setting Custom Properties
  4. Real-World Use Case
  5. Conclusion


The System.setProperty() method is a static method in the System class that sets the value of the specified system property. System properties are key-value pairs that provide information about the runtime environment and can be used to configure the behavior of Java applications.

setProperty() Method Syntax

The syntax for the setProperty() method is as follows:

public static String setProperty(String key, String value)


  • key: The name of the system property.
  • value: The value to be associated with the system property.


  • 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 system property.
  • NullPointerException if key or value is null.


Basic Usage

To demonstrate the basic usage of setProperty(), we will set a custom system property and retrieve its value.


public class SetPropertyExample {
    public static void main(String[] args) {
        // Set a custom system property
        System.setProperty("", "customValue");

        // Retrieve and print the custom system property
        String propertyValue = System.getProperty("");
        System.out.println("Custom Property: " + propertyValue);


Custom Property: customValue

Modifying Existing Properties

You can use the setProperty() method to modify existing system properties.


public class ModifyPropertyExample {
    public static void main(String[] args) {
        // Set an initial value for a system property
        System.setProperty("", "initialValue");

        // Modify the system property
        String previousValue = System.setProperty("", "newValue");

        // Print the previous and current values
        System.out.println("Previous Value: " + previousValue);
        System.out.println("Current Value: " + System.getProperty(""));


Previous Value: initialValue
Current Value: newValue

Setting Custom Properties

You can set multiple custom properties to configure the behavior of your application.


public class CustomPropertiesExample {
    public static void main(String[] args) {
        // Set multiple custom properties
        System.setProperty("app.mode", "development");
        System.setProperty("db.url", "jdbc:mysql://localhost:3306/mydb");

        // Retrieve and print the custom properties
        System.out.println("App Mode: " + System.getProperty("app.mode"));
        System.out.println("Database URL: " + System.getProperty("db.url"));


App Mode: development
Database URL: jdbc:mysql://localhost:3306/mydb

Real-World Use Case

Configuring Application Settings

In a real-world scenario, you might want to configure application settings using system properties. This approach allows you to change the behavior of your application without modifying the source code.


public class ConfigExample {
    public static void main(String[] args) {
        // Set system properties for configuration
        System.setProperty("config.env", "production");
        System.setProperty("log.level", "DEBUG");

        // Retrieve and use the configuration properties
        String env = System.getProperty("config.env");
        String logLevel = System.getProperty("log.level");

        System.out.println("Configuration Environment: " + env);
        System.out.println("Log Level: " + logLevel);

        // Use the configuration properties in the application
        if ("production".equals(env)) {
            // Production-specific logic
            System.out.println("Running in production mode.");
        } else {
            // Development-specific logic
            System.out.println("Running in development mode.");

        if ("DEBUG".equals(logLevel)) {
            // Enable debug logging
            System.out.println("Debug logging enabled.");
        } else {
            // Disable debug logging
            System.out.println("Debug logging disabled.");


Configuration Environment: production
Log Level: DEBUG
Running in production mode.
Debug logging enabled.


The System.setProperty() method in Java provides a way to set the value of specific system properties. By understanding how to use this method, you can configure the behavior of your Java applications dynamically. Whether you are setting custom properties, modifying existing properties, or managing configuration settings, the setProperty() method offers used for working with system properties in Java.