||(Or) Logical Operator in Java vs .Net [closed]

Question

I have been coding in Java(Mainly) and .Net for a while.

What I found is that the || logical operator in .Net is different in result to the || operator in Java.

Lets look at the following Java code:

Object obj = null;

if(obj == null || obj.toString().isEmpty()){
    System.out.println("Object is null");
}

The result of the code above will be:

Object is null

The reason for that is because obj == null is true and the second expression wasn't evaluated. If it was, I would have received a java.lang.NullPointerException.

And if I used the single or (|) I would also received a NullPointerException (Both are evaluated).

My question is the following:

If the code was C#, I will always get a ObjectReferenceNotSet etc. exception because the obj value is null and the second expression is always evaluated (Regardless of the operator), meaning the result is different in C# than in Java. If I would to change the C# code to work properly, I have to create two if statements.

Is there not an easier way to do this in C# to be similar to Java? (Keep it in one if with 2 expressions)

Thank you.

Answer 1

The || operator in C# is short-circuiting, just like in Java. As is &&. The | and & operators are not short-circuiting, just like in Java.

If your results are different, there is a bug in the code. Can you show us the offending C# please?

This works fine:

    object obj = null;

    if(obj == null || string.IsNullOrEmpty(obj.ToString())) {
        Console.WriteLine("Object is null");
    }

Answer 2

The || operator has exactly the same meaning in Java and C#. It is called a conditional logical OR, or "short-circuiting" logical OR operator:

http://msdn.microsoft.com/en-us/library/6373h346%28VS.71%29.aspx

Answer 3

This behaviour is a strict java language feature:

At run time, the left-hand operand expression is evaluated first ;[...] if the resulting value is true, the value of the conditional-or expression is true and the right-hand operand expression is not evaluated. If the value of the left-hand operand is false, then the right-hand expression is evaluated; [...] the resulting value becomes the value of the conditional-or expression.

Thus, || computes the same result as | on boolean or Boolean operands. It differs only in that the right-hand operand expression is evaluated conditionally rather than always

Similar rules are defined for the java conditional-and operator.

Compare (identical) to C#:

The && and || operators are called the conditional logical operators. They are also called the “short-circuiting” logical operators.

conditional-and-expression:

• inclusive-or-expression
• conditional-and-expression && inclusive-or-expression

conditional-or-expression:

• conditional-and-expression
• conditional-or-expression || conditional-and-expression

The && and || operators are conditional versions of the & and | operators:

• The operation x && y corresponds to the operation x & y, except that y is evaluated only if x is not false.
• The operation x || y corresponds to the operation x | y, except that y is evaluated only if x is not true.

Answer 4

It's called "short circuit evaluation". There is no need to evaluate the next statement. This is a nice feature in Java.