Java - Cheat Sheet

Java Programming Terminologies

• JVM (Java Virtual Machine): executes the bytecode generated by the compiler.
• Bytecode: The Javac compiler of JDK compiles the Java source code into bytecode so that it can be executed by JVM.
• JDK (Java Development Kit): It is a complete Java development kit that includes everything including compiler, Java Runtime Environment (JRE), java debuggers, java docs, etc.
• JRE (Java Runtime Environment): allows the Java program to run, however, we cannot compile it.
• Garbage Collector: To delete or recollect that memory JVM has a program called Garbage Collector.
• Finalize method: this function is triggered by the garbage collector just before an object is deleted or destroyed.

Java Basic Types and Variables

Primitive Data Types

Let’s start off by learning the primitive data types that Java offers:

Data Type	Size	Range
byte	8	-128..127
short	16	-32,768..32,767
int	32	-2,147,483,648.. 2,147,483,647
long	64	-9,223,372,036,854,775,808.. 9,223,372,036,854,775,807
float	32	3.4e-0.38.. 3.4e+0.38
double	64	1.7e-308.. 1.7e+308
char	16	Complete Unicode Character Set
Boolean	1	True, False

String

String str1 = “Welcome”; // Using literal

String str2 = new String(”Edureka”); // Using new keyword

The java.lang.String class implements Serializable, Comparable and CharSequence interfaces. Since the String object is immutable in nature Java provides two utility classes:

1. StringBuffer: It is a mutable class that is thread-safe and synchronized.
2. StringBuilder: It is a mutable class that is not thread-safe but is faster and is used in a single threaded environment.

Flow Control

Selection statements

// if statement
if (condition) {expression} 

// if-else statement
if (condition) {expression} else {expression} 

// switch statement
switch (var) 
{ case 1: expression; break; default: expression; break; } 

Iterative statements

// for loop
for (condition) {expression}

// for each loop
for (int i: someArray) {}  

// while loop
while (condition) {expression} 

// do while loop
do {expression} while(condition)

Reference

https://www.geeksforgeeks.org/java-cheat-sheet/#java-programming-terminologies