2.DataTypes Control Statements Operators

8/4/2019 2.DataTypes Control Statements Operators

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I Career Craft

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Data Types and Control Statements


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Data Types


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Built-in Data Types

Java primitives (whole numbers)

byte

short

intlong

Java primitives (real numbers)

float

double


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Built-in Data Types

Java primitives (text)

char (character, use single quotes: b)

String *

Java primitives (True/False)boolean

* String is not a primitive


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Variable Declarations

Simple form

;

Example

int total;Optional initialization at declaration

= ;

Exampleint total = 0;


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Examples

int counter;

int numStudents = 583;

float gpa;

double batAvg = .406;

char gender;

char gender = f;

boolean isSafe;

boolean isEmpty = true;

String personName;

String streetName = North Avenue;


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Primitive Type Facts

Type Size Min Defaultboolean false

Max1bit false* true*

char '\u0000' (null)2

byte (byte) 01 -128 127

short (short) 02 -32,768 32,767

int 04 -2,147,483,648 2,147,483,647

long 0L8 -9,223,372,036,854,775,808 9,223,372,036,854,775,807

float 0.0F4 Approx3.4E+38 with 7 significant digits

double 0.0D8 Approx1.7E+308 with 15 significant digits

void

* Not truly min and max. Note: Size is in Bytes


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Conditionals & Iteration


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Decision Statements

if statement omitting else branch:

if (condition)

statement1;

if statement omitting else branch:

if (condition) {

statements;

} // if


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Decision Statements

if statement - single statement bodies:if (condition)

statement1;

else

statement2;

if statement - multiple statement blocks:if (condition) {

statements;

}

else {statements;

} // if


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Multiple Selections via switch

1. Use if construct for single selection.

2. Use if/else construct for double selection.

3. Use switch construct for multiple selection.

Notes about switch:

Useful when making a selection amongmultiple values of the same variable.

Not useful when selecting among valuesof different variables.


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Switch syntax

switch (){

case :

// whatever code you want

break; // usually need this

case :

// whatever code you want

break; // usually need this

default:

// whatever code you wantbreak; // optional

}


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Multiple Selections via switch

Note the "optional" default case at the end of the switch statement.It is technically optional onlyin terms of syntax.

switch (number) {

case 1:

System.out.println ("One");

break;

case 2:

System.out.println ("Two");

break;

case 3:

System.out.println ("Three");

break;

default:System.out.println("Not 1, 2, or 3");

break; // Needed???

} // switch

For safety and good programming practice,alwaysinclude a 'default' case.

This mightwork without

the defaultcase, but

would bepoor

technique


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How many days?

if (month == 4 || month == 6 ||

month == 9 || month == 11)

numdays = 30;

else if (month = 2)

{

numdays = 28;

if (leap)

numdays = 29;

}

else

numdays = 31;


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Switch

switch (month)

{

case 4:

case 6:

case 9:

case 11:numdays = 30;

break;

case 2:

numdays = 28;

if(leap)numdays = 29;

break;

default: /* Good idea? */

numdays = 31;

}


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Java example:

while (condition){

}

Java Iteration Constructs: "While Loops"

Note: Check is made before entering loop thus it is possible that loop may notexecute


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Java example:

do

{

statement 1;

...

statement N;

} while (condition);

Java Iteration Constructs: "Do While Loops"

Test Last Loop: Body of loop is guaranteed to be executed at least once.Useful when termination condition is developed inside loop.


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Java Iteration Constructs: For Loop

Java example:

int count;

for (count = 1; count


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Secret!A for Loop can always be converted to awhile loop

i = 0;

while (i < 10)

{

System.out.println(i);

i++;

}

for(i = 0; i < 10; i++)

{

System.out.println(i);

}

This will help you understand the sequence of operationsof a for loop


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Operators


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Operators based on the number ofoperators:

Unary Operators

Binary Operators

Ternary Operators


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Arithmetic Operators

Sign Unary Operators + -

Increment and Decrement Operators ++ --

Basic Arithmetic Operators + - * / %


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Relational Operators

Greater than (>)

Less than (=)

Less than or equal to (


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Logical Operators

Bitwise Operators

Short-circuit operators


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Bitwise Logical Operators

AND (&)

OR (|)

XOR (^)

Bitwise Inversion (~)`


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Short-Circuit Logical Operators

Short-circuit Logical AND (&&)

Short-circuit Logical OR OR (||)

Boolean Inversion-NOT (!)


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Assignment Operators

= +=

-=

*=

/=

%=

&=

|=

^=


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Advanced Operators

Shortcut if-else statement (?:)

Dot operator (.)

Cast operator ()

new

instanceof


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Equality

Equality of primitives (==)

Equality of references (==)

Equality of object (equals)


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Arrays


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A problem with simple variables

One variable holds one valueThe value may change over time, but at anygiven time, a variable holds a single value

If you want to keep track of many values, youneed many variables

All of these variables need to have names

What if you need to keep track of hundreds orthousands of values?


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Multiple values

An array lets you associate one name with a fixed (butpossibly large) number of values

All values must have the same type

The values are distinguished by a numerical index between 0and array size minus 1

12 43 6 83 14 -57 109 12 0 60 1 2 3 4 5 6 7 8 9

myArray


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Indexing into arrays

To reference a single array element, usearray-name[ index]

Indexed elements can be used just like simple variables

You can access their values

You can modify their valuesAn array index is sometimes called a subscript

12 43 6 83 14 -57 109 12 0 6

0 1 2 3 4 5 6 7 8 9

myArray

myArray[0] myArray[5] myArray[9]


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Using array elements

Examples:x = myArray[1]; // sets x to 43

myArray[4] = 99; // replaces 14 with 99

m = 5;

y = myArray[m]; // sets y to -57

z = myArray[myArray[9]];// sets z to 109

12 43 6 83 14 -57 109 12 0 6

0 1 2 3 4 5 6 7 8 9

myArray


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Array values

An array may hold anytype of value

All values in an array must be the sametype

For example, you can have:

An array of integers

An array of StringsAn array of PersonAn array of arrays of StringsAn array of Object


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Two ways to declare arrays

You can declare more than one variable in the same declaration:int a[ ], b, c[ ], d; // notice position of brackets

a and c are int arrays

b and d are justints

Another syntax:int [ ] a, b, c, d; // notice position of brackets

a, b, c anddare int arrays

When the brackets come before the first variable, they apply toallvariables in the list


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Different ways of Creating the array

int myarray [ ]= {1,2,3}; Only Values

int myarray [ ]= new int[3]; Only size of array

myarray[0]=1;

myarray[1]=2;myarray[2]=3;

int myarray [ ]= new int[] {1,2,3}; No size, only values


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How to retrieve the values

To retrieve the values from an array

for (int i=0; i < myarray.length; i++)

{

System.out.println(Value is: + myarray[i]);}

Here lengthindicates the size of an array


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Arrays of objects

Suppose you declare and define an arrayof objects:

Person[ ] people = new Person[20];

There is nothing wrong with this array, butit has 20 referencesto Persons in it

all of these references are initially null

you have not yetdefined 20 PersonsFor example, people[12].name will give

you a nullPointerException


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Arrays of arrays

The elements of an array can be arrays

Once again, there is a special syntax

Declaration: int[ ][ ] table; (or int table[ ][ ];)

Definition: table = new int[10][15];

Combined: int[ ][ ] table = new int[10][15];The first index (10) is usually called the row index; the secondindex (15) is the column index

An array like this is called a two-dimensional array


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Different ways of creating array of arrays

int[ ][ ] table = { {1, 2}, {3, 6}, {7, 8} };

int[ ][ ] table = new int[3][2];

Int[ ][ ] table = new int[ ][ ] { {1, 2}, {3, 6}, {7, 8} };

1 2

3 6

7 8

0 1

0

1

2

For example, table[1][1] contains 6

table[2][1] contains8,andtable[1][2]is array out of bounds

To retrieve the values:

for (int i = 0; i < 3; i++)

{ for (int j = 0; j < 2; j++)

{System.out.println ( table[i][j] );

}

}


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Size of these arrays

int[ ][ ] table = new int[3][2];

The length of this array is the number of rows:table.length is3

Each row contains an array

To get the number of columns, pick a row and ask forits length:

table[0].lengthis 2

But remember, rows may not all be the samelength

1 2

3 6

7 8

0 1

0

1

2

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2.DataTypes Control Statements Operators