How to define an equals method (object equality) in Scala

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 4.15, “How to define an equals method (object equality) in Scala.”


You want to define an equals method for a Scala class so you can compare object instances to each other.

How to compare String equality in Java

Java String comparison FAQ: Can you share some examples of how to compare strings in Java?

If you’re like me, when I first started using Java, I wanted to use the == operator to test whether two String instances were equal, but that’s not the correct way to do it in Java.

In Scala you compare Strings with '==', not 'equals'

Scala String FAQ: How do you compare string equality in Scala?

In Scala you compare two Strings with the == operator. This is different than Java, where you compare two Strings with the equals method.

For example, given these strings:

A Java instanceof array example alvin September 20, 2009 - 12:00am

While working with various "Java instanceof" tests recently, my curiosity was piqued, and I thought I'd take a look at how the instanceof operator works when testing against a Java array.

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 if, else, elsif ("else if") syntax

Summary: This tutorial shows a collection of Perl if, else, and else if examples.

Here are some examples of the Perl if/else syntax, including the “else if” syntax, which is really elsif. (I wrote this because after working with many different languages I can never remember the “else if” syntax for most languages, and elsif is pretty rare.)

The Perl if/else syntax

The Perl if/else syntax is standard, I don’t have any problems here:

Perl ‘equals’ FAQ: What is true and false in Perl?

Perl true/false FAQ: What is true in Perl? What is false in Perl?

The Perl programming language is a little unusual in not having true and false boolean operators. Because of this, I can never seem to remember what equates to true and false in Perl, so I decided to create this page.

What is true/false in Perl

In short, the following elements evalue to false in Perl:

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:

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.


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: