Asserting

Checking arithmetic with assert

a = 1 - Math.abs(1 - a % 2);

// This will throw an error if my arithmetic above is wrong.
assert a >= 0 && a <= 1 : "Calculated value of " + a + " is outside of expected bounds";

return a;

Syntax

• assert expression1;
• assert expression1 : expression2;

Parameters

|Parameter|Details |---|---|---|---|---|---|---|---|---|--- |expression1|The assertion statement throws an AssertionError if this expression evaluates to false. |expression2|Optional. When used, AssertionErrors thrown by the assert statement have this message.

Remarks

By default, assertions are disabled at runtime.

To enable assertions, you must run java with -ea flag.

java -ea com.example.AssertionExample

Assertions are statements that will throw an error if their expression evaluates to false. Assertions should only be used to test code; they should never be used in production.