Comparing Java and Ruby
Java and Ruby are both open source languages ranked in the top 20 of the TIOBE index for most popular programming languages, at spots 2 and 13, respectively, for June 2020.
If you want to learn a new programming language and are trying to decide between these two, let’s explore which may be more useful for you.
Interpreted vs. compiled
Ruby is an interpreted language, meaning code is not first compiled into bytecode files separately. Ruby source code is interpreted directly at runtime and compiled into an instruction set, and the instructions are subsequently run on the Ruby virtual machine (VM).
Java, in contrast, is a compiled language. First, a Java compiler compiles the source code into bytecode. A Java source code file (.java file) is compiled using the javac application into a bytecode file (.class file). The class file contains the bytecode and is run on a Java VM using the java application.
An interpreted language has the benefit of not requiring a compiler and generating an intermediate bytecode file. A compiled language has the advantage of being able to perform compile-time syntax, type checking, and other performance optimizations.
Dynamically typed vs. statically typed
Ruby is a dynamically typed language. It provides no static data types that could be associated with variables in Ruby source code. Ruby supports built-in data types for all kinds of data, including numbers, strings, arrays, hashes, boolean, and nil. At runtime the appropriate data types are used dynamically to interpret the code and convert it to a VM instruction set.
The main advantage of a dynamically typed language is the flexibility it provides in being able to develop code without declaring or requiring any static data types. The main disadvantage is an increased likelihood of runtime errors and somewhat reduced performance.
Java is a statically typed language with support for several primitive data types (int, byte, short, char, long, double, float, and boolean) in addition to class and interface types and arrays. Java is a strongly typed language, and every variable must be associated with a type. Type inferencing was introduced in Java version 10 where a variable may be declared without an explicit type; by using the var keyword, the compiler inferences the type from the context.
The main advantage of static data typing is being able to perform compile-time type checking, reducing the likelihood of runtime errors.
Both Ruby and Java are object-oriented languages with support for inheritance. In Ruby, everything evaluates to an object—including statements, expressions, control-flow structures, methods, constants, variables, operators, and keywords. In Java, only instances of classes and arrays are objects.
Neither Java nor Ruby support multiple inheritance, so a class cannot extend to more than one other class at a time.
Nested classes and interfaces
Java supports nested classes, or declared classes within classes. They are class members, just like fields and methods. The main benefits of nested classes are a logical grouping of classes, increased encapsulation, and a more easily understood code that is also easier to maintain. Ruby has no notion of nested classes.
Java also supports interfaces, and Ruby doesn’t.
Other differences in syntax and constructs also exist, but these are the main differences that are most relevant to common uses for Java and Ruby.