Java System Properties
Quick Reference Guide Java System Property

The Java System Property accepts a boolean value (true or false)

Default Value

false Explained

If the java application prefers to only use IP version 4 (IPv4), then you can set the system property:

When the property is true, it is impossible for the application to connect to a host that only supports IPv6.

According to the Java Networking Documentation:

If IPv6 is available on the operating system the underlying native socket will be, by default, an IPv6 socket which lets applications connect to, and accept connections from, both IPv4 and IPv6 hosts.

Related System Properties

The system property is related to the property, however it would be used to prefer IPv6 over IPv4 network connections.

Here are some other networking Java system properties:

Supported Since

Java has supported the system property since at least version 8, support may go back to even older versions of java.

Setting on Startup

You can set the java system property during startup of the java runtime using the -D command line argument:

java MyAppMain

You may also be able to specify via the JAVA_TOOL_OPTIONS environment variable:

Setting / Reading at Runtime

You can set at runtime with the following Java code:

System.setProperty("", "true");

WARNING: Depending on the property and JVM version using setProperty may or may not work if the JDK Java class that uses this variable has already been loaded. The value of the system property may be cached within an internal private static variable of the implementing class.

To read the value of at runtime, you can use this Java code:

String propertyValue = System.getProperty("");
if (propertyValue != null) {
    System.out.println(" = " + propertyValue);
} else {
    System.out.println(" was null");