2.DataTypes ControlStatements Operators

8/7/2019 2.DataTypes ControlStatements Operators

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RENAISSANCE SOFTLABS (P) LTDRENAISSANCE SOFTLABS (P) LTD


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Data Types


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Built-in Data Types

Java primitives (whole numbers)Java primitives (whole numbers)

bytebyte

shortshort

intintlonglong

Java primitives (real numbers)Java primitives (real numbers)

floatfloat

doubledouble


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Built-in Data Types

Java primitives (text)Java primitives (text)

char (character, use single quotes: b)char (character, use single quotes: b)

String *String *

Java primitives (True/False)Java primitives (True/False)

booleanboolean

* String is not a primitive* String is not a primitive


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Variable Declarations

Simple formSimple form

; ;

ExampleExample

int total;int total;

Optional initialization at declarationOptional initialization at declaration

= ; = ;

ExampleExample

int total = 0;int total = 0;


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Examples

int counter;int counter;

int numStudents = 583;int numStudents = 583;

float gpa;float gpa;

double batAvg = .406;double batAvg = .406;

char gender;char gender;

char gender = f;char gender = f;

boolean isSafe;boolean isSafe;

boolean isEmpty = true;boolean isEmpty = true;

String personName;String personName;

String streetName = North Avenue;String streetName = North Avenue;


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Primitive Type Facts

Type Size Min Default

boolean false

Max

1bit false* true*

char '\u0000' (null)2

byte (byte) 01 -128 127short (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 Approx 3.4E+38 with 7 significant digits

double 0.0D8 Approx 1.7E+308 with 15 significant digits

void

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


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Condition

als & Iteration


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Decision Statements

if statementif statement omitting else branch:omitting else branch:

if (condition)if (condition)

statement1;statement1;

if statementif statement omitting else branch:omitting else branch:

iif (condition)f (condition) {{

statements;statements;}} // if// if


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Decision Statements

if statementif statement -- single statement bodies:single statement bodies:

if (condition)if (condition)


elseelse


if statementif statement -- multiple statement blocks:multiple statement blocks:

if (condition)if (condition) {{

statements;statements;

}}

elseelse {{statements;statements;

}} // if// if


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Multiple Selections via switch

1.1. Use if construct for single selection.Use if construct for single selection.

2.2. Use if/else construct for double selection.Use if/else construct for double selection.

3.3. Use switch construct for multiple selection.Use switch construct for multiple selection.

Notes about switch:Notes about switch:

Useful when making a selection amongUseful when making a selection among

multiple values of the same variable.multiple values of the same variable.

Not useful when selecting among valuesNot useful when selecting among values

of different variables.of different variables.


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Switch syntax

switch ()switch ()

{{

case :case :

// whatever code you want// whatever code you want

break;break; // usually need this// usually need thiscase :case :


break;break; // usually need this// usually need this

default:default:


break;break; // optional// optional

}}


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Multiple Selections via switch

Note the "optional" default case at the end of the switch statement.

It is technically optionalIt is technically optional onlyonlyin terms of syntax.in 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, always include a 'default' case.

This might

work without

the default

case, but

would be

poor

technique


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How many days?

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

month == 9 || month == 11)month == 9 || month == 11)

numdays = 30;numdays = 30;

else if (month = 2)else if (month = 2){{


if (leap)if (leap)


}}

elseelse



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Switch

switch (month)switch (month)

{{

case 4:case 4:

case 6:case 6:

case 9:case 9:

case 11:case 11:numdays = 30;numdays = 30;

break;break;

case 2:case 2:


if(leap)if(leap)numdays = 29;numdays = 29;

break;break;

default:default: /* Good idea? *//* Good idea? */


}}


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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 not

execute


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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 a while loop

i = 0i = 0;;

while (while (i < 10i < 10)){{

System.out.println(i);System.out.println(i);

i++;i++;

}}

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

{{System.out.println(i);System.out.println(i);

}}

This will help you understand the sequence of operations

of a forloop


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OperatorsOperators


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Operators based on the number ofOperators based on the number ofoperators:operators:

Unary OperatorsUnary Operators

Binary OperatorsBinary Operators

Ternary OperatorsTernary Operators


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Arithmetic Operators

Sign Unary OperatorsSign Unary Operators

++

--

Increment and Decrement OperatorsIncrement and Decrement Operators

++++

----

Basic Arithmetic OperatorsBasic Arithmetic Operators

++

--

**

//

%%


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Relational Operators

Greater than (>)Greater than (>)

Less than (=)

Less than or equal to (


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Logical Operators

Bitwise OperatorsBitwise Operators

ShortShort--circuit operatorscircuit operators


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Bitwise Logical Operators

AND (&)AND (&)

OR

(|)OR

(|)

XOR (^)XOR (^)

Bitwise Inversion (~)`Bitwise Inversion (~)`


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Short-Circuit Logical Operators

ShortShort--circuit Logical AND (&&)circuit Logical AND (&&)

ShortShort--circuit Logical O

ROR

(||)circuit Logical OR

OR

(||)

Boolean InversionBoolean Inversion--NOT (!)NOT (!)


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Assignment Operators

==

+=+=

--==

*=*= /=/=

%=%=

&=&=

|=|= ^=^=


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Advanced Operators

Shortcut ifShortcut if--else statement (?else statement (?:):)

Dot operator (.)Dot operator (.)

Cast operator ()Cast operator ()

newnew

instanceofinstanceof


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Equality

Equality of primitives (==)Equality of primitives (==)

Equality of references (==)

Equality of references (==)

Equality of object (equals)Equality of object (equals)


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Arrays


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A problem with simple variables

One variable holds one valueOne variable holds one value

The value may change over time, but at anyThe value may change over time, but at anygiven time, a variable holds a single valuegiven time, a variable holds a single value

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

All of these variables need to have namesAll of these variables need to have names

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


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Multiple values

AnAn arrayarray lets you associate one name with a fixed (butlets you associate one name with a fixed (but

possibly large) number of valuespossibly large) number of values

All values must have the same typeAll values must have the same type

The values are distinguished by a numericalThe values are distinguished by a numerical indexindex between 0between 0

and array size minus 1and array size minus 1

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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Indexing into arrays

To reference a single array element, useTo reference a single array element, use

arrayarray--namename [[indexindex]]

Indexed elements can be used just like simple variablesIndexed elements can be used just like simple variables

You can access their valuesYou can access their values

You can modify their valuesYou can modify their valuesAn array index is sometimes called aAn array index is sometimes called a subscriptsubscript

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

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

m = 5;m = 5;

y = myArray[m];y = myArray[m]; // sets y to// sets y to --5757

z = myArray[myArray[9]];z = myArray[myArray[9]];// sets z to 109// 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 holdAn array may hold anyanytype of valuetype of value

All values in an array must be theAll values in an array must be the samesame typetype

For example, you can have:For example, you can have:

An array ofAn array ofintegersintegersAn array ofAn array ofStringsStringsAn array ofAn array ofPersonPersonAn array of arrays ofAn array of arrays ofStringsStringsAn array ofAn array ofObjectObject


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Two ways to declare arrays

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

aa andand cc areare intint arraysarrays

bb andand dd are justare just intintss

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

aa,, bb,, cc andand dd areare intint arraysarrays

When the brackets come before the first variable, they apply toWhen the brackets come before the first variable, they apply toallallvariables in the listvariables in the list


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Different ways of Creating the array

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

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

myarray[0]=1;myarray[0]=1;

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

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


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How to retrieve the values

To retrieve the values from an arrayTo retrieve the values from an array

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

{{

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

HereHere lengthlength

indicates the size of an arrayindicates the size of an array


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Arrays of objects

Suppose you declare and define an arraySuppose you declare and define an array

of objects:of objects:

Person[ ] people = new Person[20];Person[ ] people = new Person[20];

There is nothing wrong with this array, butThere is nothing wrong with this array, but

it has 20it has 20 referencesreferences to Persons in itto Persons in it

all of these references are initiallyall of these references are initially nullnull

you haveyou have not yetnot y

etdefined 20 Personsdefined 20 Persons

For example,For example, people[12].namepeople[12].name will givewill give

you ayou a nullPointerExceptionnullPointerException


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Arrays of arrays

The elements of an array can be arraysThe elements of an array can be arrays

Once again, there is a special syntaxOnce again, there is a special syntax

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

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

Combined:Combined: int[ ][ ] table = new int[10][15];int[ ][ ] table = new int[10][15];The first index (The first index (1010) is usually called the) is usually called the rowrow index; the secondindex; the second

index (index (1515) is the) is the columncolumn indexindex

An array like this is called aAn array like this is called a twotwo--dimensional arraydimensional array


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Different ways of creating array of arrays

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

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

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

1 2

3 6

7 8

0 1

0

1

2

For example,For example, table[1][1]table[1][1] containscontains 66

table[2][1]table[2][1] containscontains 88,, andand

table[1][2]table[1][2] is array out of boundsis array out of bounds

To retrieve the values:To retrieve the values:

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

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

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

}}

}}


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Size of these arrays

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

The length of this array is the number ofThe length of this array is the number ofrows:rows:

table.lengthtable.length isis 33

Each row contains an arrayEach row contains an array

To get the number ofTo get the number ofcolumns,columns, pick a row and ask forpick a row and ask forits length:its length:

table[0].lengthtable[0].length isis 22

But remember, rows may not all be the sameBut remember, rows may not all be the same

lengthlength

1 2

3 67 8

0 1

0

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