Java Programming/Keywords/assert

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assert is a Java keyword used to define an assert statement. An assert statement is used to declare an expected boolean condition in a program. If the program is running with assertions enabled, then the condition is checked at runtime. If the condition is false, the Java runtime system throws a AssertionError.

Assertions may be declared using the following syntax:

Computer code
assert expression1 [: expression2];

expression1 is a boolean that will throw the assertion if it is false. When it is thrown, the assertion error exception is created with the parameter expression2 (if applicable).

An example:

Computer code
assert list != null && list.size() > 0 : "list variable is null or empty";
Object value = list.get(0);

Assertions are usually used as a debugging aid. They should not be used instead of validating arguments to public methods, or in place of a more precise runtime error exception.

Assertions are enabled with the Java -ea or -enableassertions runtime option. See your Java environment documentation for additional options for controlling assertions.