Enabling and Disabling Assertions

By default, assertions are disabled. Two command-line switches allow you to selectively enable or disable assertions.

The following switch enables assertions at various granularities:

java [ -enableassertions | -ea  ] [:<package name>"..." | :<class name> ]

With no arguments, the switch enables assertions by default. With one argument ending in "...", assertions are enabled in the specified package and any subpackages by default. If the argument is simply "...", assertions are enabled in the unnamed package in the current working directory. With one argument not ending in "...", assertions are enabled in the specified class.

The following switch disables assertions in similar fashion:

java [ -disableassertions | -da ] [:<package name>"..." | :<class name> ]

If a single command line contains multiple instances of these switches, they are processed in order before loading any classes. For example, to run a program with assertions enabled only in package com.wombat.fruitbat (and any subpackages), the following command could be used:

java -ea:com.wombat.fruitbat... java -ea:com.wombat.fruitbat... <Main class>

To run a program with assertions enabled in package com.wombat.fruitbat but disabled in class com.wombat.fruitbat.Brickbat, the following command could be used:

java -ea:com.wombat.fruitbat... -da:com.wombat.fruitbat.Brickbat <class>

The above switches apply to all class loaders, and to system classes (which do not have a class loader). There is one exception to this rule: in their no-argument form, the switches do not apply to system classes. This makes it easy to turn on asserts in all classes except for system classes. A separate switch is provided to enable asserts in all system classes (i.e., to set the default assertion status for system classes to true).

 java [ -enablesystemassertions | -esa ]

For symmetry, a corresponding switch is provided to enable asserts in all system classes.

java [ -disablesystemassertions | -dsa ]