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
##Java Statements (cont)
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
##java.util.ArrayList Methods
add(itm) Add itm to list
get(i) Return ith item
size() Return number of items
remove(i) Remove ith item
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<StÂrinÂg,String> names =
new HashMap<StÂrinÂg, String>();
HashMap.html for more.ava 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
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
##ava 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);