java Cheet Sheet

Java Fundamentals Cheat Sheet 

Java cheet sheet

Java Fundamentals

Java Data Types byte / short / int / long -123, 10 float / double 235.13 char 'U' boolean true, false String "­Gre­etings from earth" Java Statements If Statement if ( expression ) {  ­ statements } else if ( expression ) {  ­ statements } else {  ­ statements } While Loop while ( expression ) {  ­ statements } Do-While Loop do {  ­ statements } while ( expression ); For Loop for ( int i = 0; i < max; ++i) {  ­ statements } For Each Loop for ( var : collection ) {  ­ statements } Switch Statement switch ( expression ) {  ­ case value:  ­ ­ ­ statements  ­ ­ ­ ­break;  ­ case value2:  ­ ­ ­ statements  ­ ­ ­ ­break;  ­ ­def­ault:  ­ ­ ­ statements } Exception Handling try {  ­ ­sta­tem­ents; } catch (Except­ionType e1) {  ­ ­sta­tem­ents; } catch (Exception e2) {  ­ ­cat­ch-all statem­ents; } finally {  ­ ­sta­tem­ents; }

Java Data Conver­sions String to Number int i = Intege­r.p­ars­eInt(str); double d = Double.pa­rse­Double(str); Any Type to String String s = String.va­lueOf(value); Numeric Conver­sions int i = (int) numeric expression; Java String Methods s.length() length of s s.charAt(i) extract ith character s.subst­ring(start, end) substring from start to end-1 s.toUpp­erC­ase() returns copy of s in ALL CAPS s.toLow­erC­ase() returns copy of s in lowercase s.indexOf(x) index of first occurence of x s.replace(old, new) search and replace s.split(regex) splits string into tokens s.trim() trims surrou­nding whitespace s.equals(s2) true if s equals s2 s.compa­reTo(s2) 0 if equal/+ if s > s2/- if s < s2 See codingnija100 java.u­til.Ar­rayList Methods l.add(itm) Add itm to list l.get(i) Return ith item l.size() Return number of items l.remove(i) Remove ith item l.set(i, val) Put val at position i ArrayL­ist­<St­rin­g> names =  ­ new ArrayL­ist­<St­rin­g>(); java.u­til.Ha­shMap Methods m.put(key,value) Inserts value with key m.get(key) Retrieves value with key m.conta­insKey(key) true if contains key HashMa­p<S­t­­rin­Â­g­,St­rin­g> names =  ­ new HashMa­p<S­t­­rin­g, String­>(); See codingninja100

Java Hello World import java.u­til.Date; public class Hello {  ­ ­public static void main(S­tring[] args) {  ­ ­ ­ ­Sys­tem.ou­t.p­rin­tln­("Hello, world!­");  ­ ­ ­ Date now = new Date();  ­ ­ ­ ­Sys­tem.ou­t.p­rin­tln­("Time: " + now);  ­ } } * Save in Hello.java * Compile: javac Hello.java * Run: java Hello Java Arithmetic Operators x + y add x - y subtract x * y multiply x / y divide x % y modulus ++x / x++ increment     --x / x-- decrement Assignment shortcuts: x op= y Example: x += 1 increments x Java Comparison Operators x < y Less x <= y Less or eq x > y Greater x >= y Greater or eq x == y Equal x != y Not equal Java Boolean Operators ! x (not) x && y (and) x || y (or) Java Text Formatting printf style formatting System.ou­t.p­rin­tf(­"­Count is %d\n", count); s = String.fo­rma­t("Count is %d", count); Messag­eFormat style formatting s = Messag­eFo­rma­t.f­ormat(  ­ ­"At {1,time}, {0} eggs hatche­d.",  ­ 25, new Date()); Individual Numbers and Dates s = Number­For­mat.ge­tCu­rre­ncy­Ins­tance()  ­ .fo­rma­t(x); s = new Simple­Dat­eFo­rma­t(""h:mm a"")  ­ .fo­rma­t(new Date()); s = new Decima­lFo­rma­t("#­,##­0.0­0")  ­ .fo­rma­t(1­25.32); See codingninja100

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