Cheat Sheets

Java Cheat Sheet

Quick reference for Java — data types, strings, arrays, loops, collections, classes, exception handling, and more.

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Getting Started
Hello WorldPrintCommentsImport
Primitive Data Types
intlongdoublefloatbooleancharbyteshort
Variables & Type Casting
Declare & assignWidening castNarrowing castString → intString → doubleint → Stringvar (Java 10+)
Strings
CreateConcatenateLengthcharAt()indexOf()substring()toUpperCase()toLowerCase()trim()replace()contains()startsWith()endsWith()equals()isEmpty()split()StringBuilder
Arrays
Declare & initDeclare with sizeAccess elementLengthSortTo string2D array2D access
Operators
ArithmeticIncrementDecrementComparisonLogicalAssignmentTernaryinstanceofBitwise
Conditionals
if / else if / elseswitchswitch expression (Java 14+)
Loops
for loopenhanced for (for-each)while loopdo-while loopbreakcontinue
Collections
ArrayListHashMapHashSetLinkedListArrayDequeIterate mapCollections.sort()
Classes & Objects
Class definitionCreate objectthis keywordInheritanceInterfaceStatic methodGetter / Setter
Exception Handling
try / catch / finallythrows declarationthrowCommon exceptions
Access Modifiers
publicprotecteddefault (package-private)privatefinalstatic
Math Methods
max() / min()abs()pow()sqrt()round()random()floor() / ceil()
User Input
Scanner setupRead stringRead intRead doubleClose scanner