Documenting and Checking Assumptions

<aside> 💡 Functions may have constraints on its parameters.

</aside>

• We could check for these constraints by throwing an exception on checking the condition for the constraints on the parameters

  public static double myfunc(double x) throws IllegalArgumentException{
  	// To Assume x >= 0
  	if( x < 0){
  		throw new IllegalArgumentException("x<0");
  	}
  }
  

• If myfunc is only used internally in our own code.

  • The errors should only be flagged during development and debugging.
  • This diagnostic code should not trigger at runtime.

• Solution: Assert the property you assume to hold.

Assertions

<aside> 💡 If assertions fails, code throws AssertionError

</aside>

public static double myfunc(double x){
	assert x >= 0 : x;
}

<aside> 💡 This exception SHOULD NOT be CAUGHT.

</aside>

• Can also provide additional information to be printed with diagnostic message.

Enabling and Disabling Assertions

<aside> 💡 Assertions are enabled or disabled at runtime.

</aside>

• It does not require recompilation.

• Use the following flag to run with assertions enabled:

  java -enableassertions MyCode

Can also use -ea as abbreviation for -enableassertions/tu

Can selectively turn on assertions for a class: java -ea:Myclass MyCode

Can selectively turn on assertions for a package: java -ea:in.ac.iitm.onlinedegree MyCode

Also, Disable assertions globally or selectively: java -disableassertions MyCode

java -da:Myclass MyCode

Can combine as:

java -ea in.ac.iitm.onlinedegree -da:Myclass MyCode

Separate switch to enable assertions for system classes: java -enablesystemassertions MyCode

or java -esa MyCode