equals

A Java “instanceof null” example

You might think that when the Java instanceof operator is used to test a null reference, such as a null reference to a String, instanceof would realize that even though the reference is currently null, it is a reference to a String, so you might expect instanceof to return true ... but it doesn't.

Perl comparison operators

Perl equality FAQ: Can you share a list of the Perl equality operators?

Sure. Here's a convenient list of the Perl comparison operators (also known as Perl equality operators, equal, or not equal operators).

The Perl comparison operators are different for numeric and string comparison tests, as you can see in the following table:

Unix/Linux shell script reference page

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Linux shell script test syntax

All of the shell script tests that follow should be performed between the bracket characters [ and ], like this:

if [ true ]
then
  # do something here
fi

Very important: Make sure you leave spaces around the bracket characters.

I'll show more detailed tests as we go along.

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To perform tests on files use the following comparison operators:

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Eclipse can generate Java hashCode and equals methods

A nice feature of Eclipse is that you can easily generate hashCode and equals methods for your Java class using the editor. You'll really appreciate this capability when you need to create these methods whenever you're doing anything related to sorting, comparisons, comparators, etc.

A Java method that tests if a String is null or blank

Problem: You're working on a Java application, and you're repeatedly performing a test to determine whether a String (or many strings) are either blank or null.

Solution

Create a simple Java method to perform this test for you. The following Java method returns true if a String is blank or null, otherwise it returns false: