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For the following conditionals:
if (a != null && a instanceof A)
or
if (a instanceof A)
Is there any advantage (for example, performance-wise) to check for null first? Both conditionals should be equal in result.
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Null means nothing. No object. At all. A null value can be assigned to an object reference of any type. Null can be cast to any type as it can be assigned to an object reference of that type.
Use an "if" statement to create a condition for the null. You can use the boolean value as a condition for what the statement does next. For example, if the value is null, then print text "object is null". If "==" does not find the variable to be null, then it will skip the condition or can take a different path.
equalsIgnoreCase(String) is null-safe with literal string on left side of method' completed without exception!
equals(null) will always be false. The program uses the equals() method to compare an object with null . This comparison will always return false, since the object is not null .
No advantage whatsoever, you can just do with
if(a instanceof A) {}
this will return evaluate to false if a is null
59
if(a instanceof A) is enough.
The if(a!=null && expr) pattern is used when expr will throw a NullPointerException if a is null. a instanceof A doesn't throw a NPE and just returns false if a is null.
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