Selected Operators and Their Precedence
(See Appendix B for the complete list.)
[]
Array element access
++ -- !
Increment, decrement, Boolean not
* / %
Multiplication, division, remainder
+ -
Addition, subtraction
< <= > >=
Comparisons
== !=
Equal, not equal
&&
Boolean and
||
Boolean or
=
Assignment
Conditional Statement
if (floor >= 13)
{
actualFloor = floor - 1;
}
else if (floor >= 0)
{
actualFloor = floor;
}
else
{
System.out.println("Floor negative");
}
Condition
Executed when condition is true
Second condition (optional)
Executed when
all conditions are
false (optional)
Class Declaration
public class CashRegister
{
private int itemCount;
private double totalPrice;
public void addItem(double price)
{
itemCount++;
totalPrice = totalPrice + price;
}
. . .
}
Method
Instance variables
do
{
System.out.print("Enter a positive integer: ");
input = in.nextInt();
}
while (input <= 0);
for (double value : values)
{
sum = sum + value;
}
An array or collection
Executed for each element
Loop body executed
at least once
Set to a new element in each iteration
Executed while
condition is true
Condition
Initialization Condition Update
Loop Statements
while (balance < TARGET)
{
year++;
balance = balance * (1 + rate / 100);
}
for (int i = 0; i < 10; i++)
{
System.out.println(i);
}
String Operations
String s = "Hello";
int n = s.length(); // 5
char ch = s.charAt(1); // 'e'
String t = s.substring(1, 4); // "ell"
String u = s.toUpperCase(); // "HELLO"
if (u.equals("HELLO")) ... //
Use
equals
, not
==
for (int i = 0; i < s.length(); i++)
{
char ch = s.charAt(i);
Process
ch
}
Mathematical Operations
Math.pow(x, y)
Raising to a power x
y
Math.sqrt(x)
Square root x
Math.log10(x)
Decimal log log
10
(x)
Math.abs(x)
Absolute value |x|
Math.sin(x)
Math.cos(x)
Sine, cosine, tangent of x (x in radians)
Math.tan(x)
Variable and Constant Declarations
int cansPerPack = 6;
final double CAN_VOLUME = 0.335;
Type Name Initial value
Parameter
type and name
Exits method and
returns result.
Return typeModiers
Method Declaration
public static double cubeVolume(double sideLength)
{
double volume = sideLength * sideLength * sideLength;
return volume;
}
Input
Scanner in = new Scanner(System.in);
//
Can also use
new Scanner(new File("input.txt"));
int n = in.nextInt();
double x = in.nextDouble();
String word = in.next();
String line = in.nextLine();
while (in.hasNextDouble())
{
double x = in.nextDouble();
Process
x
}
Linked Lists, Sets, and Iterators
LinkedList<String> names = new LinkedList<>();
names.add("Bob"); //
Adds at end
ListIterator<String> iter = names.listIterator();
iter.add("Ann"); //
Adds before current position
String name = iter.next(); //
Returns
"Ann"
iter.remove(); //
Removes
"Ann"
Set<String> names = new HashSet<>();
names.add("Ann"); //
Adds to set if not present
names.remove("Bob"); //
Removes if present
Iterator<String> iter = names.iterator();
while (iter.hasNext())
{
Process
iter.next()
}
Arrays
int[] numbers = new int[5];
int[] squares = { 0, 1, 4, 9, 16 };
int[][] magicSquare =
{
{ 16, 3, 2, 13},
{ 5, 10, 11, 8},
{ 9, 6, 7, 12},
{ 4, 15, 14, 1}
};
for (int i = 0; i < numbers.length; i++)
{
numbers[i] = i * i;
}
for (int element : numbers)
{
Process element
}
System.out.println(Arrays.toString(numbers));
//
Prints
[0, 1, 4, 9, 16]
Element
Element type type Length
All elements are zero.
Maps
Map<String, Integer> scores = new HashMap<>();
scores.put("Bob", 10);
Integer score = scores.get("Bob");
for (String key : scores.keySet())
{
Process
key
and
scores.get(key)
}
Key type Value type
Returns
null
if key not present
Output
System.out.print("Enter a value: ");
System.out.println("Volume: " + volume);
System.out.printf("%-10s %10d %10.2f", name, qty, price);
try (PrintWriter out = new PrintWriter("output.txt"))
{
Write to
out
}
Left-justied string Integer Floating-point number
Field width Precision
Does not advance to new line.
Use
+
to concatenate values.
The output is closed at the end of
the
try
-with-resources statement.
Use the
print
/
println
/
printf
methods.
Array Lists
ArrayList<String> names = new ArrayList<String>();
names.add("Ann");
names.add("Cindy"); // [Ann, Cindy], names.size()
is now 2
names.add(1, "Bob"); // [Ann, Bob, Cindy]
names.remove(2); // [Ann, Bob]
names.set(1, "Bill"); // [Ann, Bill]
String name = names.get(0); //
Gets
"Ann"
System.out.println(names); //
Prints
[Ann, Bill]
Element type
(optional)
Use wrapper type,
Integer
,
Double
,
etc., for primitive types.
Add elements to the end
Initially empty
bj6_insidecovers_8x10.indd 1 4/30/15 3:48 PM
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