java Basic Programming Needs

Contents…
Data Types
Type Conversion and Casting
Variables
Scope and lifetime of variables
Operators
Expressions
Control Statements

DATA TYPES
• Variables are nothing but reserved memory
locations to store values. This means that
when you create a variable you reserve
some space in memory.

• Based on the data type of a variable, the
operating system allocates memory and
decides what can be stored in the reserved
memory

Data Types
• There are two data types available in Java:
Primitive Data Types
Reference/Object Data Types

byte:
Byte data type is a 8-bit signed two.s complement integer.
Minimum value is -128 (-2^7)
Maximum value is 127 (inclusive)(2^7 -1)
Default value is 0
Byte data type is used to save space in large arrays, mainly in place
of integers, since a byte is four times smaller than an int.
Example : byte a = 100 , byte b = -50

short:
Short data type is a 16-bit signed two's
complement integer.
Minimum value is -32,768 (-2^15)
Maximum value is 32,767(inclusive) (2^15 -1)
Default value is 0.
Example : short s= 10000 , short r = -20000

int:
Int data type is a 32-bit signed two's complement integer.
Minimum value is - 2,147,483,648.(-2^31)
Maximum value is 2,147,483,647(inclusive).(2^31 -1)
Int is generally used as the default data type for integral values
unless there is a concern about memory.
The default value is 0.
Example : int a = 100000, int b = -200000

long:
Long data type is a 64-bit signed two's complement integer.
Minimum value is -9,223,372,036,854,775,808.(-2^63)
Maximum value is 9,223,372,036,854,775,807 (inclusive). (2^63 -
1)
This type is used when a wider range than int is needed.
Default value is 0L.
Example : int a = 100000L, int b = -200000L

float:
Float data type is a single-precision 32-bit IEEE 754 floating point.
Float is mainly used to save memory in large arrays of floating point
numbers.
Default value is 0.0f.
Float data type is never used for precise values such as currency.
Example : float f1 = 234.5f

double:
double data type is a double-precision 64-bit IEEE 754 floating point.
This data type is generally used as the default data type for decimal
values. generally the default choice.
Double data type should never be used for precise values such as
currency.
Default value is 0.0d.
Example : double d1 = 123.4

boolean:
boolean data type represents one bit of information.
There are only two possible values : true and false.
This data type is used for simple flags that track
true/false conditions.
Default value is false.
Example : boolean one = true

char:
char data type is a single 16-bit Unicode character.
Minimum value is 'u0000' (or 0).
Maximum value is 'uffff' (or 65,535 inclusive).
Char data type is used to store any character.
Example . char letterA ='A'

Reference Datatypes
• Reference variables are created using defined
constructors of the classes. They are used to access
objects. These variables are declared to be of a specific
type that cannot be changed. For
example, Employee, Puppy etc.

• Class objects, and various type of array variables come
under reference data type.

• Default value of any reference variable is null.

• A reference variable can be used to refer to any object of
the declared type or any compatible type.

• Example : Animal animal = new Animal("giraffe");

Data Types
DataType Memory (Bytes) Range
byte 1 -128 to 127
short 2 -32768 t0 32767
int 4 -2147483648 to 2147483647
long 8 -922337263685477808 to
-922337263685477807
float 4 1.4e-045 to 3.4e+038
double 8 4.9e-324 to 1.8e+308
char 2 0 to 65536
boolean - True/False

TYPE CONVERSION
 Size Direction of Data Type
 Widening Type Conversion (Casting down)
 Smaller Data Type  Larger Data Type
 Narrowing Type Conversion (Casting up)
 Larger Data Type  Smaller Data Type

 Conversion done in two ways
 Implicit type conversion
 Carried out by compiler automatically
 Explicit type conversion
 Carried out by programmer using casting

Type Conversion

 Widening Type Converstion
 Implicit conversion by compiler automatically

byte -> short, int, long, float, double
short -> int, long, float, double
char -> int, long, float, double
int -> long, float, double
long -> float, double
float -> double

Type Conversion

 Narrowing Type Conversion
 Programmer should describe the conversion
explicitly
byte -> char
short -> byte, char
char -> byte, short
int -> byte, short, char
long -> byte, short, char, int
float -> byte, short, char, int, long
double -> byte, short, char, int, long, float

Type Casting

• General form: (targetType) value
Examples:
1) integer value will be reduced module bytes
range:
int i;
byte b = (byte) i;
2) floating-point value will be truncated to
integer value:
float f;
int i = (int) f;

VARIABLES
• type identifier [ = value][, identifier [= value] ...] ;
• Here are several examples of variable declarations of various
types
int a, b, c; // declares three ints, a, b, and c.
int d = 3, e, f = 5; // declares three more ints, initializing
// d and f.
byte z = 22; // initializes z.
double pi = 3.14159; // declares an approximation of pi.
char x = 'x'; // the variable x has the value 'x'.

Types of variables
There are three kinds of variables in Java:
Local variables
Instance variables
Class/static variables

Local variables are declared in methods, constructors, or blocks
Instance variables are declared in a class, but outside a
method, constructor or any block.
Class variables also known as static variables are declared with
the static keyword in a class, but outside a
method, constructor or a block.

Scope Definition
A scope is defined by a block:

{
…
}

A variable declared inside the scope is not visible outside:

{
int n;
}
n = 1;

Example: Variable Scope
class Scope {
public static void main(String args[]) {
int x;
x = 10;
if (x == 10) {
int y = 20;
System.out.println("x and y: " + x + “ " + y);

x = y * 2;
}
System.out.println("x is " + x + “y is” + y);
}
}

Variable Lifetime
Variables are created when their scope is entered by control flow and
destroyed when their scope is left:

1) A variable declared in a method will not hold its value between different
invocations of this method.

2) A variable declared in a block looses its value when the block is left.
3) Initialized in a block, a variable will be re-initialized with every re-entry.

Variables lifetime is confined to its scope!

Example: Variable Lifetime
class LifeTime {
int x;
for (x = 0; x < 3; x++) {
int y = -1;
System.out.println("y is: " + y);
y = 100;
System.out.println("y is now: " + y);
}
}
}

OPERATOR TYPES
• Java operators are used to build value expressions.
• Java provides a rich set of operators:
1) arithmetic (+,-,*,/,%)
2) assignment (+=,-=,*=,/=,%=,=)
3) relational (==,!=,<,>,<=,>=)
4) logical (&&,||,!)
5) bitwise (&,|,~,^,<<,>>,>>)

Bit wise operators
~ ~op Inverts all bits

& op1 & op2 Produces 1 bit if both operands are 1

| op1 |op2 Produces 1 bit if either operand is 1

^ op1 ^ op2 Produces 1 bit if exactly one operand is 1

>> op1 >> op2 Shifts all bits in op1 right by the value of
op2
<< op1 << op2 Shifts all bits in op1 left by the value of
op2

Other Operators
?: shortcut if-else statement

[] used to declare arrays, create arrays, access array elements

. used to form qualified names

(params) delimits a comma-separated list of parameters

(type) casts a value to the specified type

new creates a new object or a new array

instanceof determines if its first operand is an instance of the second

Table: Operator Precedence
highest
() [] .
++ -- ~ !
* / %
+ -
>> >>> <<
> >= < <=
== !=
&
^
|
&&
||
?:
= op=
lowest

Expressions
• An expression is a construct made up of
variables, operators, and method invocations, which are
constructed according to the syntax of the language, that
evaluates to a single value.

• Examples of expressions are in bold below:
int number = 0;
anArray[0] = 100;
System.out.println ("Element 1 at index 0: " + anArray[0]);
int result = 1 + 2; // result is now 3 if(value1 == value2)
System.out.println("value1 == value2");

CONTROL STATEMENTS

• Java control statements cause the flow of execution to
advance and branch based on the changes to the state
of the program.
• Control statements are divided into three groups:

1) selection statements allow the program to choose
different parts of the execution based on the outcome
of an expression
2) iteration statements enable program execution to
repeat one or more statements
3) jump statements enable your program to execute in a
non-linear fashion

Selection Statements

• Java selection statements allow to control the flow
of program’s execution based upon conditions
known only during run-time.
• Java provides four selection statements:
1) if
2) if-else
3) if-else-if
4) switch

Iteration Statements

• Java iteration statements enable repeated
execution of part of a program until a certain
termination condition becomes true.
• Java provides three iteration statements:
1) while
2) do-while
3) for
4) for each(JDK1.5 version)

• if-else

Syntax Example

if (<condition-1>) { int a = 10;
// logic for true condition-1 goes here if (a < 10 ) {
} else if (<condition-2>) { System.out.println(“Less than 10”);
// logic for true condition-2 goes here } else if (a > 10) {
} else { System.out.pritln(“Greater than 10”);
// if no condition is met, control } else {
comes here System.out.println(“Equal to 10”);
} }

Result: Equal to 10s

• switch

Syntax Example

switch (<value>) { int a = 10;
case <a>: switch (a) {
// stmt-1 case 1:
break; System.out.println(“1”);
case <b>: break;
//stmt-2 case 10:
break; System.out.println(“10”);
default: break;
//stmt-3 default:
System.out.println(“None”);

Result: 10

• do-while
Syntax Example
do { int i = 0;
// stmt-1 do {
} while (<condition>); System.out.println(“In do”); i++;
} while ( i < 10);

Result: Prints “In do” 11 times

• while
Syntax Example

while (<condition>) { int i = 0;
//stmt while ( i < 10 ) {
} System.out.println(“In while”); i++;
}

Result: “In while” 10 times

• for

Syntax Example

for ( initialize; condition; expression) for (int i = 0; i < 10; i++)
{ {
// stmt System.out.println(“In for”);
} }

Result: Prints “In do” 10 times

Jump Statements

• Java jump statements enable transfer of
control to other parts of program.
• Java provides three jump statements:
1) break (3 uses:loop,switch,nested blocks)
2) continue
3) return
• In addition, Java supports exception
handling that can also alter the control flow
of a program.

TEST

I m not giving the answers for these basic questions,

please try and execute if possible. If you still want the answers

then copy and paste the entire question in google .

What all gets printed when the following program is compiled and run.
Select the two correct answers.

public class test
{
public static void main(String args[])
{
int i, j=1; i = (j>1)?2:1;
switch(i)
{
case 0: System.out.println(0); break;
case 1: System.out.println(1);
}
}
}
a) 0
b) 1
c) 2
d) 3

Which declaration of the main method below
would allow a class to be started as a
standalone program. Select the one correct
answer.

a) public static void main(String args[])
b) public static void MAIN(String args[])
c) public static void main(String args)
d) public static void main(char args[])
e) static public void main(String args[])
f) public static int main(char args[])

Which of the following will compile without error

1) import java.awt.*;
package Mypackage;
class Myclass {}

2) package MyPackage;
import java.awt.*;
class MyClass{}

3) /*This is a comment */
package MyPackage;
import java.awt.*;
class MyClass{}

What’s the difference between
constructors and normal methods?

Constructors must have the same name
as the class and can not return a value.
They are only called once
while regular methods could be called many
times and it can return a value or can be
void.

• Give a simplest way to find out the time a
method takes for execution without
using any profiling tool?

long start = System.currentTimeMillis ();
method ();
long end = System.currentTimeMillis ();

System.out.println (“Time taken for execution is ” + (end –
start));

public class test
{
{
String s1 = "abc";
String s2 = "abc";
if(s1 == s2)
System.out.println(1);
else
if(s1.equals(s2))
else
}
}
a)1
b)2
c)3
d)4

• Which of the following are legal array
declarations. Select the three correct
answers.

a) int i[5][];
b) int i[][];
c) int []i[];
d) int i[5][5];
e) int[][] a;

What is the range of values that can be
specified for an int. Select the one correct
answer. The range of values is compiler
dependent.

a) -231 to 231 - 1
b) -231-1 to 231
c) -215 to 215 - 1
d) -215-1 to 215

What would be the results of compiling and running the following
class. Select the one correct answer.

class test
{
public static void main()
{
System.out.println("test");
}
}

a)The program does not compile as there is no main method
defined.
b)The program compiles and runs generating an output of "test"
c)The program compiles and runs but does not generate any
output.
d)The program compiles but does not run.

What gets printed when the following program is compiled and
run. Select the one correct answer.

class test {
int i,j,k,l=0;
k = l++;
j = ++k;
i = j++;
System.out.println(i);
}
}

a) 0
b) 1
c) 2
d) 3

• Which operator is used to perform bitwise
inversion in Java. Select the one correct
answer.

a) ~
b) !
c) &
d)|
e) ^

What gets printed when the following program is compiled and run. Select the one
correct answer.

public class test {
byte x = 3;
x = (byte)~x;
System.out.println(x);
}
}

a) 3
b) 0
c) 1
d) 11
e) 252
f) 214
g) 124
h) -4

What gets displayed on the screen when the following program is compiled and
run. Select the one correct answer.

public class test {
int x,y;
x = 3 & 5;
y = 3 | 5;
System.out.println(x + " " + y);
}
}

a) 7 1
b) 3 7
c) 1 7
d) 3 1
e) 1 3
f) 7 3
g) 7 5

What all gets printed when the following program is compiled
and run. Select the one correct answer.

public class test {
{
int i=0, j=2;
do {
i=++i;
j--;
}
while(j>0);
System.out.println(i);
}
}
a) 0
b) 1
c) 2
d) The program does not compile because of statement "i=++i;"

What gets displayed on the screen when the following program is
compiled and run. Select the one correct answer.

public class test {
int x, y;

x = 5 >> 2;
y = x >>> 2;
System.out.println(y);
}
}

a) 5
b) 2
c) 80
d) 0
e) 64

java Basic Programming Needs

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java Basic Programming Needs