com.google.java.contract

Annotation Type Ensures

@Documented
@Target(value={METHOD,CONSTRUCTOR})
@Retention(value=RUNTIME)
public @interface Ensures

Specifies postconditions that apply to the annotated method. The annotated method must establish its postconditions if and only if the preconditions were satisfied.

When run time checking of contracts is enabled, postconditions are checked at method exit, when the method exits normally, of the and throw a PreconditionError when they are violated. Postconditions are not checked when the method exits by throwing an exception.

See Also:

ThrowEnsures

Required Element Summary

Required Elements

Modifier and Type	Required Element and Description
java.lang.String[]	value The list of postconditions that must be met by the annotated method, written as strings.

Element Detail

value

public abstract java.lang.String[] value

The list of postconditions that must be met by the annotated method, written as strings. The expressions must be valid Java code and can reference all things visible to the class, as well as the method's arguments. Since postconditions may need to refer to the old value of an expression and the value returned by the annotated method, the following extensions are allowed:

The keyword result refers to the value returned from the method, if any. It is an error to have a method parameter named result.

The old(expression) pseudo-method construct refers to the value of its argument before execution of the method. expression must be a balanced expression, with regard to parentheses. The old() construct is preprocessed using the following simple rules (similar to macro expansion done by a C preprocessor):

• the word old, followed by an opening parenthesis, is recognized as an identifier;
• the enclosed expression is only parsed for balanced parentheses;
• textual substitution is used.

It is an error to call a method named old from within a postcondition.