Chapter i(introduction to java)

History of Java programming
• A programming language originally developed by James Gosling at Sun
Microsystems .
• Java is a cross-platform language that enables you to write programs for many
different operating systems
• syntax : C and C++ but has a simplerobject model and fewer lowlevel facilities .
• Oak=>Green=>Java
• Java enables users to develop and deploy applications on the Internet for servers,
desktop computers, and small hand-held devices, applications on the server side,
Web server to generate dynamic Web pages

• javac SomeApplication.java

JCreator
Java Developing Tools: TextPad, NetBeans, or Eclipse integrated support
development environment (IDE)

1. multiline comment: /* and end with */.
2. single-line comment or end-of-line comment : // I hate java
3. documentation comment: /** and ends with */
Comment

Test1public class Test1{
public static void main(String[] args)
{
/* For */
System.out.println("Computer Bactouk Center");
}
}
Ex2:
public class Welcome4
{
// main method begins execution of Java application
public static void main( String args[] )
{
System.out.printf( "%sn%sn", "Welcome to", "Java Programming!" );
} // end method main
} // end class Welcome4

public(access specifier) class Test1(identifier)
{
{
System.out.println("Computer Bactouk Center");
}
}
 public means that it is accessible by any other classes
 static means that it is unique.
 void is the return value but void means nothing which means there will be no return
value .
 main is the name of the method
 (String[] args) is used for command line parameters.
 Curly brackets are used again to group the contents of main together .
 static allows main( ) to be called without having to instantiate a particular instance of
the class
 Methods are able to perform tasks and return information
 A string is sometimes called a character string, a message or a string literal.
 System.out is known as the standard output object.
 “Computer Backtouk Center” is argument.
Class block
Method
block

import java.util.*;
public class TestJava {
public static void main(String[] args) {
Scanner sc=new Scanner(System.in);
int a;
a=sc.nextInt();
System.out.println(a);
}
}
Note: sc.nextDouble(), sc.next()
• import declaration that helps the compiler locate a class that is used in this program.
Reading Input from the Console

Step1: Compiler
• The javac compiler creates a file called
Example.class(C:>javac Example.java)
• Program is run, the following output is
displayed()(C:>java Example)

Variables
• Variables are used to store values to be used later in a program. They are called
variables because their values can be changed.
• Variables are for representing data of a certain type. To use a variable, you declare
it by telling
• the compiler its name as well as what type of data it can store. The variable
declaration tells
• the compiler to allocate appropriate memory space for the variable based on its
data type.
• The variable is the basic unit of storage, combination of an identifier, a type, and an
optional initializer.
• type identifier [ = value][, identifier [= value] ...] ;
– int a, b, c;
– int d = 3, e, f = 5;
– byte z;
– z = 22;
– double d = 3.14159;
– char x = 'x'; //’x’ is initialize constant

Named Constants
• The value of a variable may change during the execution of a program, but a named
constant or simply constant represents permanent data that never changes.
– final datatype CONSTANTNAME = VALUE;
public class ComputeArea
{
{
final double PI; // Declare a constant
PI=100;
// Assign a radius
double radius = 20;
// Compute area
double area = radius * radius * PI;
// Display results
System.out.println("The area for the circle of radius " + radius + " is " + area);
}
}

Data type
• The Primitive Types
Primitive type Data Type
Integer byte
short
int
long
Characters char
Boolean boolean

Integer
public class DayTime
{
{
int point1;
int point2;
point1=10;
point2=200;
int day=30;
System.out.println("From " + point1 + "km to " + point2 + "km is " +
(point2-point1) + "km");
System.out.println("From " + point1 + " to " + point2 + "km, we take " + day + "
days");
}
}

Char
• Char in java is 0 to 65,536
• Char in C is 0 to 127(Not IBM computer)
• Char in C is 0 to 255(IBM computer)
public class TestA
{
{
char ch1='A';
char ch2=97;
System.out.println("ch1=" + ch1 + "nch2=" + ch2);
}
}

Character Escape
- Suppose you want to print a message with quotation marks in the output. Can you
write a statement like this?

Floating-point numbers
public class Area
{
{
double pi, r, a;
r = 21.2;
pi = 3.1416;
a = pi * r * r;
System.out.println("Area of circle is " + a);
}
}

Floating-point numbers
public class Calc
{
{
float v1=6;
float v2=4.3f;
System.out.println(v1 + "+" + v2 + "=" + (v1+v2));
System.out.println(v1 + "-" + v2 + "=" + (v1-v2));
System.out.println(v1 + "*" + v2 + "=" + (v1*v2));
System.out.println(v1 + "/" + v2 + "=" + (v1/v2));
System.out.println(v1 + "%" + v2 + "=" + (v1%v2));
}
}
• Floating-point literals are written with a decimal point. By default, a floating-point literal is
treated as a double type value. For example, 5.0 is considered a double value, not a float value.
You can make a number a float by appending the letter f or F, and you can make a number a
double by appending the letter d or D. For example, you can use 100.2f or 100.2F for a float
number, and 100.2d or 100.2D for a double number

boolean
• True/false
public class Area
{
{
boolean sleep=true; sleep=false;
System.out.printf("I am so tired so feel seep("
+ sleep + ")");
}
}

boolean
public class TestA
{
{
int a=10,b=100;
System.out.println(a>b);
}
}

Note: Java Strings
• To represent a string of characters, use the data type called String.
• objects designed to represent a sequence of characters.
• In Java, ordinary strings are objects of the class String.
• A string literal is a sequence of characters between double quotes.
– String s=new String();
• S=“sdfsdf”
– String s=new String(“Texto”);
– String s=“texto”;
• String s=“texto”
• s=s + “libre”
• If one of the operands is a nonstring (e.g., a number), the nonstring value is
converted into a string and concatenated with the other string.
• EX:
– String message = "Welcome " + "to " + "Java";
– String s = "Chapter" + 2; // s becomes Chapter2
– String s1 = "Supplement" + 'B'; // s1 becomes SupplementB
• Method: next() and nextLine()?
• == check to see if the two string are exactly the same object
• .equals() // . equalsIgnoreCase() method check if the two strings have the same
value;

Equality and relational operators
• Tertiary Operator
Result=(condition)?TrueReturn:FalseReturn;

Dynamic Initialization
public class TestA
{
{
double x=100.0;
double result=Math.sqrt(x);
System.out.println("result sqrt(x)=" + result);
}
}

The Scope and Lifetime of Variables
public class TestA
{
public static void main(String args[])
{
int x; // known to all code within main
x = 10;
if(x == 10)
{ // start new scope
in y = 20; // known only to this block
// and y both known here.
System.out.println("x and y: " + x + " " + y);
x = y * 2;
}
// y = 100; // Error! y not known here
// x is still known here.
int y=30;
System.out.println("x is " + x);
System.out.println("y is " + y);
}
}

The Scope and Lifetime of Variables
public class TestA
{
{
int x;
for(x = 0; x < 3; x++)
{
int y = -1; // y is initialized each time block is entered
System.out.println("y is: " + y); // this always prints -1
y = 100;
System.out.println("y is now: " + y);
}
}
}

Type Conversion and Casting
• narrowing conversion
– if you want to assign an int value to a byte variable? This
conversion will not be performed automatically, because a
byte is smaller than an int.
– Explicit cast statement: v1=(type)v2;
• Automatic Conversions
– int type is always large enough to hold all valid byte
values, so no explicit cast statement .
byte a = 40;
byte b = 50;
byte c = 100;
int d = a * b / c;

narrowing conversion
• int a; byte b; b = (byte) a;
• Casting Incompatible Types
public class JavaTest {
{
int a;
byte b;
a=10;
b = (byte)a;
System.out.println(b);
a=10;
b=(byte)a;
System.out.println(b);
}
}

narrowing conversion
public class JavaTest {
{
byte b;
int i = 257;
double d = 323.142;
System.out.println("nConversion of int to byte.");
b = (byte) i;
System.out.println("i and b " + i + " " + b);
System.out.println("nConversion of double to int.");
i = (int) d;
System.out.println("d and i " + d + " " + i);
System.out.println("nConversion of double to byte.");
b = (byte) d;
System.out.println("d and b " + d + " " + b);
}
}

Automatic Conversions
public class JavaTest
{
{
double b;
int i = 257;
double d = 323.142;
System.out.println("nConversion of int to byte.");
b = i;
System.out.println("i and b " + i + " " + b);
System.out.println("nConversion of double to int.");
i = (int) d;
System.out.println("d and i " + d + " " + i);
System.out.println("nConversion of double to byte.");
b = d;
System.out.println("d and b " + d + " " + b);
}
}

Formatting Console Output
• to format the output using the printf method.
– System.out.printf(format, item1, item2, ..., itemk)
* (int)(Math.random() *10)
returns a random single-digit integer (i.e., a
number between 0 and 9)

import java.util.Scanner;
public class SubtractionQuiz {
int number1 = (int)(Math.random() * 10);
{
int temp = number1;
number1 = number2;
number2 = temp;
}
System.out.print ("What is " + number1 + " - " + number2 + "? ");
Scanner input = new Scanner(System.in);
System.out.println("You are correct!");
else
System.out.println("Your answer is wrongn" + number1 + " - “ +
number2 + " should be " + (number1 - number2));
}}

Reference data type
• array type
• class type
• interface type

Array
• An array is a special kind of object that contains values called
elements. The java array enables the user to store the values of the
same type in contiguous memory allocations.
• One-Dimensional Arrays
– a list of like-typed variables
– Step:
• Declaration : type array-var[ ];
• Allocate : array-var = new type[size];
• Assign value: array_var[n]=value;
– Or step
• Declaration and Allocate: type arr-var[]=new type[size];
• Assign value: array-var[n]=values;
– Or step
• Declaration + Allocate + Assign: type arr-var[]={v1,v2,v3…vn};
• Note: array_var.length

One-Dimensional Arrays
public class JavaTest
{
{
String arr_Day[];
arr_Day=new String[7];//or Sring arr_Day=new String[7];
arr_Day[0]="Monday";
arr_Day[1]="Tuesday";
arr_Day[2]="Wednesday";
arr_Day[3]="Thursday";
arr_Day[4]="Friday";
arr_Day[5]="Saturday";
arr_Day[6]="Sunday";
System.out.println("Today is " + arr_Day[5]);
}
}

One-Dimensional Arrays
public class TestJava
{
{
int month_days[];
month_days = new int[12];
month_days[0] = 31;
month_days[1] = 28;
month_days[2] = 31;
month_days[3] = 30;
month_days[4] = 31;
month_days[5] = 30;
month_days[6] = 31;
month_days[7] = 31;
month_days[8] = 30;
month_days[9] = 31;
month_days[10] = 30;
month_days[11] = 31;
System.out.println("April has " + month_days[3] + " days.");
}
}
Copy Array:
int[] sourceArray = {2, 3, 1, 5, 10};
int[] targetArray = new int[sourceArray.length];
for (int i = 0; i < sourceArray.length; i++)
{
targetArray[i] = sourceArray[i];
}

Passing array to Method
public static void printArray(int[] array){
for (int i = 0; i < array.length; i++) {
System.out.print(array[i] + " ");
}}
printArray(new int[]{3, 1, 2, 6, 4, 2});
//===============
int x = 1; // x represents an int value
int[] y = new int[10]; // y represents an array of int values
//y[0]=100;
m(x, y); // Invoke m with arguments x and y
System.out.println("x is " + x);
System.out.println("y[0] is " + y[0]);
}
public static void m(int number, int[] numbers) {
number = 1001; // Assign a new value to number
numbers[0] = 5555; // Assign a new value to numbers[0]
}

Return array From Method
public static int[] reverse(int[] list) {
int[] result = new int[list.length];
for (int i = 0, j = result.length - 1;i < list.length; i++, j--) {
result[j] = list[i];
}
return result;
}
int[] list1 = {1, 2, 3, 4, 5, 6};
int[] list2 = reverse(list1);

Multidimensional Arrays(Two Diemensional)
• are actually arrays of arrays
• two-dimensional array to store a matrix
– elementType arrayRefVar[][] = new elementType[nR][nC];
– elementType[][] arrayRefVar;
• arrayRefVar = new elementType[nR][nC];
– elementType arrayRefVar[][];
• arrayRefVar = new elementType[nR][nC];
– elementType[][] arrayRefVar = {{….},{….},….,{…}}
– arrayRefVar.length => Length of row
– arrayRefVar[index].length => Length of column
EX:
• for (int i = 0; i < matrix.length; i++) {
for (int j = 0; j < matrix[i].length; j++) {
int i1 = (int)(Math.random() * matrix.length);
int j1 = (int)(Math.random() * matrix[i].length);
// Swap matrix[i][j] with matrix[i1][j1]
int temp = matrix[i][j];
matrix[i][j] = matrix[i1][j1];
matrix[i1][j1] = temp;
}}

public class JavaMe {
int marr[][]=new int[2][4];
marr[0][0]=0;
marr[0][1]=1;
marr[0][2]=2;
marr[0][3]=3;
marr[1][0]=0;
marr[1][1]=1;
marr[1][2]=2;
marr[1][3]=3;
System.out.println(marr[0][0] + "t" + marr[0][1] + "t" + marr[0][2] +
"t" + marr[0][3] +"nr" + marr[1][0] +"t" + marr[1][1] + "t" + marr[1][2] +
"t" + marr[1][3]);
}
}
Multidimensional Arrays(Two Diemensional)

EX:
int twoD[][] ={{0,1},{2,3},{4,5},{6,7},{8,9}};
System.out.println(twoD[0][0]+ "t" + twoD[0][1] + "nr" + twoD[1][0]+ "t" + twoD[1][1]+
"nr" + twoD[2][0]+ "t" + twoD[2][1]
+ "nr" + twoD[3][0]+ "t" + twoD[3][1]+ "nr" + twoD[4][0]+ "t" +
twoD[4][1] );
}}
EX:
int twoD[][] = new int[4][];
twoD[0] = new int[1];
twoD[0][0]=0;twoD[1][0]=1;twoD[1][1]=2;twoD[2][0]=3;twoD[2][1]=4;
twoD[2][2]=5;twoD[3][0]=6; twoD[3][1]=7;twoD[3][2]=8;twoD[3][3]=9;
System.out.println(twoD[0][0] + "nr" + twoD[1][0] + twoD[1][1] + "nr" +
twoD[2][0] + + twoD[2][0] + + twoD[2][2] + "nr” + twoD[3][0] + twoD[3][1] + twoD[3][2]
+ twoD[3][3]);
}
}

Passing Two-Dimensional Arrays to Methods
• System.out.println("nSum of all elements is " + sum(m));
• public static int sum(int[][] m) {
int total = 0;
for (int row = 0; row < m.length; row++) {
for (int column = 0; column < m[row].length; column++) {
total += m[row][column];
}}
return total;}

Control Statements
• To cause the flow of execution to advance and
branch based on changes to the state of a
program.
– selection: allow your program to choose different
paths of execution based upon the outcome of an
expression or the state of a variable.
– Iteration: enable program execution to repeat one
or more statements
– jump: allow your program to execute in a
nonlinear fashion

Conditional Operator
• Ternary operator because it has three terms.
– test ? trueresult : falseresult
– Int smaller;
– smaller = x < y ? x : y;

import java.util.*;
public class TestJava{
{
int money,count;
String sheet;
System.out.print("Enter money:");money=sc.nextInt();
count=money/100;money=money%100;
sheet=count>1?"sheets":"sheet";
System.out.println("100$:" + count + " " + sheet);
}
}

Select statement
• If: be used to route program execution through two different
paths.
if (condition) statement1;
else statement2;
Ex:
int a=7, b=8;
if(a < b) a = 0;
else b = 0;

boolean dataAvailable;
if (dataAvailable)
ProcessData();
else
waitForMoreData();
--------------------------------
int bytesAvailable;
if (bytesAvailable > 0) {
ProcessData();
bytesAvailable -= n;}
else
waitForMoreData();

Nested if
if(i == 10)
{
if(j < 20) a = b;
If(k > 100) c = d; // this if is
else a = c; // associated with this else
}
else a = d; // this else refers to if(i == 10)

The if-else-if Ladder
if(condition)
statement;
else if(condition)
statement;
else if(condition)
statement;
.
.
.
else
statement;

class IfElse {
public static void main(String args[]) {
int month = 4; // April
String season;
if(month == 12 || month == 1 || month == 2)
season = "Winter";
else if(month == 3 || month == 4 || month == 5)
season = "Spring";
season = "Summer";
season = "Autumn";
else
season = "Bogus Month";
System.out.println("April is in the " + season + ".");
}
}

Converting Strings to Numbers
Convert Number to String

switch
• Provides easy way to dispatch execution to different parts of code
based on the value of an expression.
switch (expression)
{
case value1:
// statement sequence
break;
case value2:
break;
.
.
.
case valueN:
break;
default:
// default statement sequence
}
• The switch-expression must yield a value of char, byte, short, or int type and must
always be enclosed in parentheses.
• The value1, and valueN must have the same data type as the value of the switch-
expression. Note that value1, and valueN are constant expressions, meaning that
they cannot contain variables, such as 1 + x.
• char ch=(char)st.charAt(0);

class SampleSwitch
{
{
for(int i=0; i<6; i++)
switch(i) {
case 0:
System.out.println("i is zero.");
Break;
case 1:
System.out.println("i is one.");
break;
case 2:
System.out.println("i is two.");
Break;
case 3:
System.out.println("i is three.");
break;
default:
System.out.println("i is greater than 3.");
}
}}

class MissingBreak {
for(int i=0; i<12; i++)
switch(i) {
case 0:
case 1:
case 2:
case 3:
case 4:
System.out.println("i is less than 5");
break;
case 5:
case 6:
case 7:
case 8:
case 9:
System.out.println("i is less than 10");
break;
default:
System.out.println("i is 10 or more");
}
}
}

Nested switch Statements
switch(count) {
case 1:
switch(target) {
case 0:
System.out.println("target is zero");break;
case 1:
System.out.println("target is one");break;
}
break;
case 2: // ...

Switch or if?
• The switch differs from the if in that switch can only test
for equality, whereas if can evaluate any type of
Boolean expression. That is, the switch looks only for a
match between the value of the expression and one of
its case constants.
• No two case constants in the same switch can have
identical values. Of course, aswitch statement and an
enclosing outer switch can have case constants in
common.
• Aswitch statement is usually more efficient than a set of
nested ifs.

Iteration Statements
• for, while, and do-while called loop
• loop that controls how many times an operation or a
sequence of operations is performed in succession.
• A loop repeatedly executes the same set of
instructions until a termination condition is met.

While
while(condition)
{
// body of loop
}
Ex:
class While
{
{
int n = 10;
while(n >= 0)
{
System.out.println("tick " + n);
n--;//n=n-1
}
}
}

int a = 10, b = 20;
while(a > b)
System.out.println("This will not be displayed");
final int NUMBER_OF_QUESTIONS = 5;
long startTime = System.currentTimeMillis();

import java.util.*;
{
double min,n;
System.out.print("Please Enter value:");min=sc.nextDouble();
while(sc.hasNextDouble())
{
n=sc.nextDouble();
if(min>n)
min=n;
System.out.println("Min=" + min);
}
}
}

do-while
do
{
body of loop
} while (condition);
Ex:
class DoWhile {
int n = 10;
do {
n=n-2;
} while(n > 0);
}
}
- import java.io.*;
- String.substring(BeginIndex,
EndIndex)
- String.charAt(pos)

class Menu {
throws java.io.IOException {
char choice;
do {
System.out.println("Help on:");
System.out.println(" 1. if");
System.out.println(" 2. switch");
System.out.println(" 3. while");
System.out.println(" 4. do-while");
System.out.println(" 5. forn");
System.out.println("Choose one:");
choice = (char) System.in.read();
} while( choice < '1' || choice > '5');
System.out.println("n");
switch(choice) {
case '1':
System.out.println("The if:n");
System.out.println("if(condition) statement;");
System.out.println("else statement;");
break;

case '2':
System.out.println("The switch:n");
System.out.println("switch(expression) {");
System.out.println(" case constant:");
System.out.println(" statement sequence");
System.out.println(" break;");
System.out.println(" // ...");
System.out.println("}");
break;
case '3':
System.out.println("The while:n");
System.out.println("while(condition) statement;");
break;
case '4':
System.out.println("The do-while:n");
System.out.println("do {");
System.out.println(" statement;");
System.out.println("} while (condition);");
break;
case '5':
System.out.println("The for:n");
System.out.print("for(init; condition; iteration)");
System.out.println(" statement;");
break;
}}}

for
for(initialization; condition; iteration) {
// body
}
class ForTick
{
int n;
for(n=10; n>0; n--)
}
}

class ForTick
{
for(int n=10; n>0; n--)
}
}

class Comma {
int a, b;
for(a=1, b=4; a<b && a<c; a++, b--) {
System.out.println("a = " + a);
System.out.println("b = " + b);
}}}
Ex:
class ForVar {
int i;
boolean done = false;
i = 0;
for( ; !done; ) {
System.out.println("i is " + i);
if(i == 10) done = true;
i++;
}}}

The For-Each Version of the for Loop
• for(type itr-var : collection) statement-block
class ForEach {
int nums[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
int sum = 0;
// use for-each style for to display and sum the values
for(int x : nums) {
System.out.println("Value is: " + x);
sum += x;
}
System.out.println("Summation: " + sum);
}
}

class ForEach2 {
int sum = 0;
int nums[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
// use for to display and sum the values
for(int x : nums)
{
System.out.println("Value is: " + x);
sum += x;
if(x == 5) break; // stop the loop when 5 is obtained
}
System.out.println("Summation of first 5 elements: " + sum);
}
}

class ForEach3 {
int sum = 0;
int nums[][] = new int[3][5];
// give nums some values
for(int i = 0; i < 3; i++)
for(int j=0; j < 5; j++)
nums[i][j] = (i+1)*(j+1);
// use for-each for to display and sum the values
for(int x[] : nums) {
for(int y : x) {
System.out.println("Value is: " + y);
sum += y;
}
}
System.out.println("Summation: " + sum);
}
}

class Search {
int nums[] = { 6, 8, 3, 7, 5, 6, 1, 4 };
int val = 5;
boolean found = false;
// use for-each style for to search nums for val
for(int x : nums) {
if(x == val) {
found = true;
break;
}
}
if(found)
System.out.println("Value found!");
}
}

Using break
class BreakLoop {
for(int i=0; i<100; i++) {
if(i == 10) break; // terminate loop if i is 10
System.out.println("i: " + i);
}
System.out.println("Loop complete.");
}
}

class BreakLoop3 {
for(int i=0; i<3; i++) {
System.out.print("Pass " + i + ": ");
for(int j=0; j<100; j++) {
if(j == 10) break; // terminate loop if j is 10
System.out.print(j + " ");
}
System.out.println();
}
System.out.println("Loops complete.");
}
}

Using break as a civilized form of goto.
class Break {
boolean t = true;
first: {
aaaa: {
third: {
System.out.println("Before the break.");
if(t) break first; // break out of second block
System.out.println("This won't execute");
}
System.out.println("This won't execute");
}
System.out.println("This is after second block.");
}
}
}

Using continue
class Continue {
for(int i=0; i<10; i++) {
System.out.print(i + " ");
if (i%2 == 0) continue;
System.out.println("");
}
}
}

return
class Return {
boolean t = true;
System.out.println("Before the return.");
if(t) return; // return to caller
System.out.println("This won't execute.");
}
}

int num;
System.out.print("Enter number of product:");
num=sc.nextInt();
String product[][]=new String[num][5];
for(int i=0;i<num;i++)
for(int j=0;j<4;j++)
{
if(j==0) System.out.print("Enter ProdID=");
if(j==1) System.out.print("Enter ProName=");
if(j==2) System.out.print("Enter Qty=");
if(j==3) System.out.print("Enter UnitPrice=");
product[i][j]=sc.next();
}
System.out.println(" ProductID ProName Qty UnitPrice Total");
{
float price=Float.parseFloat(product[i][3]);
int qty=Integer.parseInt(product[i][2]);
float total=price*qty;
System.out.println(product[i][0] + " " + product[i][1] + " " + product[i][2] + " " +
product[i][3] + " " + total );
}
Insert

System.out.print("Enter PID to search=");String pID=sc.next();
boolean b=false;
int help=0;
{
if(product[i][0].equals(pID))
{
System.out.println("FOund");
b=true;help=I;
break;
System.out.println(“%.0f”,var);
}
}
if(b==true)
{
System.out.println(product[help][0] + " " + product[help][1] + " " +
product[help][2] + " " + product[help][3] + " " + product[help][4]);
}
if(b==false)
{
System.out.println("Not Found");
}
Search

The Math class contains the methods
• Math.pow(3.5, 2.5) returns 22.91765
• Math.sqrt(4) returns 2.0
• Math.ceil(-2.1) returns -2.0
• Math.floor(2.1) returns 2.0
• Math.max(2.5, 3) returns 3.0
• Math.min(2.5, 3.6) returns 2.5
• Math.abs(-2) returns 2

Function/Method in java
• We can do so by defining a method. The method is for creating reusable code.
• Methods are referred to as procedures and functions. A value-returning
method is called a function; a void method is called a procedure.
•
Public class TestJava{
function1body
{
function1caller;
function2caller;
}
function2body
}
• The syntax :
modifier returnValueType methodName(list of parameters) {
// Method body;}

A value-returning method
• public static float functionName([parameter..])
{
statementblock;
return value;
}
A void method
• public static void functionName([parameter..])
{
statementblock;
}

import java.util.*;
public static void getResult(byte result)
{
if(result==1)
{
System.out.println("Result point 1:");
System.out.println("|-------|");
System.out.println("| * |");
System.out.println("|-------|");
}
else if(result==2)
{
System.out.println("|---------|");
System.out.println("| * * |");
}
else if(result==3)
{
System.out.println("Result Point 3:");
System.out.println("|--------|");
System.out.println("| * * * |");
System.out.println("|--------|");
}
else if(result==4)
{
System.out.println("| * |");
}
else if(result==5)
{
System.out.println("Result point 5::");
System.out.println("| * * |");
}
else if(result==6)
{
}
}
public static void getCalc()
{
byte point, result;

import java.util.*;
public static void sum(float x, float y)
{
System.out.println(x+ "" + y + "=" + result);
}
{
float x,y,result;
System.out.print("Enter x=");x=sc.nextFloat();
System.out.print("Enter y=");y=sc.nextFloat();
sum(x,y);
}
}

Passing Primitive data type Method Argument by Value:
• The arguments must match the parameters in order, number, and compatible type, as
defined in the method signature.
• Compatible type means that you can pass an argument to a parameter without explicit
casting, such as passing an int value argument to a double value parameter.
• public static void nPrintln(String message, int n) {
for (int i = 0; i < n; i++)
System.out.println(message);
}
Passing Primitive data type Method Argument by Reference: NONE
• To generalize the foregoing discussion, a random character between any two characters
ch1 and ch2 with ch1 < ch2 can be generated as follows:
• (char)(ch1 + Math.random() * (ch2 – ch1 + 1))
’d’ – ’k’
(char)(’d’ + Math.random()*(’k’-’d’+1));
Overloading Methods
• another method with the same name but different parameters.

Chapter i(introduction to java)

Chapter i(introduction to java)

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