Intro to Java Overview Guide

Definition/Overview: Java is a high-level, secure, and multi-threaded object-oriented programming (OOP) language. It has many use cases and remains popular across many platforms/devices due to its strong compatibility/portability, as well as its memory efficiency/performance advantages in comparison to many other compiled languages. Its design is credited to James Gosling of Sun Microsystems, which has since been purchased by the Oracle Corporation.

Java is also renowned for its APIs (Application Programming Interfaces), which have both minor and major differences across Java versions. Each API contains pre-built packages and classes that can be imported into programs to provide commonly used features/functionalities.

Table of Contents

1. JVM, JRE, and JDK: Three Key Acronyms
2. Miscellaneous Keywords and Concepts
3. Supplemental Resources

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1. JVM, JRE, and JDK: Three Key Acronyms

	JVM	JRE	JDK
Term	Java Virtual Machine	Java Runtime Environment	Java Development Kit
Use Case	Byte code to machine code conversions	Executing Java apps	Developing (writing and compiling) Java code
Key Component(s)	Java byte code	JVM and libraries for Java apps	JRE and compiler (and other developer tools)
Dependency Status	Platform-Independent	Platform-Dependent	Platform-Dependent

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2. Miscellaneous Keywords and Concepts

• The static keyword creates class members that belong to a class.

  • Thus, these class members are shared among every instance of that class.
  • Non-static class members would belong to an object (an instance of the class).

• The final keyword declares constant methods and variables.

  • As they are constants, they cannot be overriden.
  • Unextendable classes can also be created.

• The this keyword is used to refer to a present instance of a class.

  • This provides differentiation between local and instance variables.

• The try keyword creates a block of code that might throw an exception.

  • The catch keyword creates a block that can handle that exception.
  • The (optional) finally keyword creates a code block to be executed even if an exception is not thrown.

• String class instances are immutable (not modifiable).

  • StringBuffer class instances are mutable.

• The .equals() method is used for comparing the content of objects.

  • The == operator is used to compare objects' references.

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3. Supplemental Resources

• Java Data Structure Leetcode Interview Questions
• Java Quick Reference Guide
• Official Java Platform SE 8 API