7. The class can be public [not compulsory]
main should be public [compulsory]
main should be static [compulsory]
return type of main should be void [compulsory]
Argument of String [] is compulsory.
only the order of public and static can be
swapped.
mohammed.sikander@cranessoftware.
com 7
9. If class is public, filename should
match class name.
If class is not public, filename can be
different.
mohammed.sikander@cranessoftware.
com 9
11. Naming Conventions
Name Convention
class Names hould start with uppercase letter and be a
noun
e.g. String, Color, Button, System, Thread etc.
interface Name should start with uppercase letter and be an
adjective e.g. Runnable, Remote, ActionListener etc.
method Name should start with lowercase letter and be a verb
e.g. actionPerformed(), main(), print(), println() etc.
variable Name should start with lowercase letter e.g.
firstName, orderNumber etc.
package Name should be in lowercase letter e.g. java, lang,
sql, util.
Constants Name should be in uppercase letter. e.g. RED,
YELLOW, MAX_PRIORITY etc.
mohammed.sikander@cranessoftware.
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12. CamelCase in java naming
conventions
Java follows camelcase syntax for
naming the class, interface, method
and variable.
If name is combined with two words,
second word will start with uppercase
letter always
actionPerformed( ),
firstName,
ActionEvent,
ActionListener etc.
mohammed.sikander@cranessoftware.
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13. Variables naming - Rules
All variable names must begin with a
letter,
an underscore ( _ ), or a dollar sign
($).
[a-z/_/$] [a-z/_/$/0-9]
Case sensitive – similar to c/c++
Samples of acceptable
variable names: YES
Samples of unacceptable
variable names: NO
Grade Grade(Test)
GradeOnTest GradeTest#1
Grade_On_Test 3rd_Test_Grade
GradeTest Grade Test (has a space)
int $a = 5;
int a$b = 8;
int _x = 4;
int _ = 9;
mohammed.sikander@cranessoftware.
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14. Variable naming – Guidelines
The convention is to always use a
letter of the alphabet. The dollar sign
and the underscore are discouraged.
Variable should begin with lowercase,
multiple word variable can use
camelCasing.
All characters in uppercase are
reserved for final(constants)
mohammed.sikander@cranessoftware.
com 14
16. Datatypes
Byte - 1 byte
Short - 2 byte
Int - 4
Long - 8
Float - 4 (IEEE 754)
Double - 8 (IEEE 754)
Char - 2 (unicode)
Boolean - 1 (size undefined)
Note : java does not support unsigned.
mohammed.sikander@cranessoftware.
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17. LITERALS
Integer literals
Decimal [1-9][0-9]
Octal 0[0-7]
Hexadecimal 0x[0-9,A-F]
Binary (JAVA SE7) 0b[0-1]
Underscore can appear in literals (JAVA SE7)
long creditCardNum =
1234_5678_9012_3456L;
Floating-point literals
Double 4.5 or 4.5d 1.23e2
Float 4.5f 1.23e2f
mohammed.sikander@cranessoftware.
com 17
18. Write the Output
class ArithmeticOperation {
public static void main(String [] args )
{
byte a = 5;
byte b = 10;
byte sum = a + b;
System.out.println("Sum = " +
sum);
}
}mohammed.sikander@cranessoftware.
com 18
int sum = a + b;
byte sum = (byte)(a +
b);
19. Write the Output
Java Program
class ArithmeticOperation {
public static void main(String [] args ) {
float res = 9 % 2.5f;
System.out.println("res = " + res);
}
}
mohammed.sikander@cranessoftware.
com 19
C/ C++ Program
int main( )
{
float res = 9 % 2.5f;
printf(" %f " ,res);
}
20. Arithmetic Operators
int / int => int
float / int => float
byte + byte => int
% operator can be applied to float-
types
Eg : 5.0 % 2.4 = 0.2
9 % 2.5 => 1.5; 10 % 2.5 => 0
mohammed.sikander@cranessoftware.
com 20
21. Output
class ArithmeticOperation {
public static void main(String [] args ) {
byte a = 5;
byte b = 10;
int sum = a + b;
byte diff = (byte)(a – b);
System.out.println("Sum = " + sum);
System.out.println(“diff = " + diff);
}
}
mohammed.sikander@cranessoftware.
com 21
22. Conversion from Small to
Large
public class Conversion {
public static void main(String args[]) {
byte b = 12;
int i = 300;
double d = 323.142;
System.out.println("nConversion of byte to int.");
i = b;
System.out.println("i and b " + i + " " + b);
System.out.println("nConversion of int to double.");
d = i;
System.out.println("d and i " + d + " " + i);
}
}
mohammed.sikander@cranessoftware.
com 22
23. Conversion from Large to
Small
public class Conversion {
public static void main(String args[]) {
byte b;
int i = 300;
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);
}
}
mohammed.sikander@cranessoftware.
com 23
24. Write the Output
public class ByteDemo {
public static void main(String [] args)
{
byte x = 127;
System.out.println(x);
x++;
System.out.println(x);
}
}
mohammed.sikander@cranessoftware.
com 24
25. Code to Print ASCII / UNICODE
Value of a Character
mohammed.sikander@cranessoftware.
com 25
public class CharAsciiValue {
public static void main(String[] args)
{
char a = 'A';
System.out.println(a + " " + (int)a);
}
}
26. Question
Consider the statement
double ans = 10.0+2.0/3.0−2.0∗2.0;
Rewrite this statement, inserting
parentheses to ensure that ans = 11.0
upon evaluation of this statement.
mohammed.sikander@cranessoftware.
com 26
27. What should be the datatype of
res variable?
public static void main( String [] args)
{
int a = 5;
int b = 10;
____ res = a > b;
System.out.println(res);
}
mohammed.sikander@cranessoftware.
com 27
28. int main( )
{
int a = 5;
if(a)
printf(“True");
else
printf(“False”);
}
public static void main(String []
args)
{
int a = 5;
if(a)
System.out.print("TRUE
");
else
System.out.print(“FALS
E");
}
mohammed.sikander@cranessoftware.
com 28
29. Relational Operators
Result of Relational operators is of type boolean.
int x = 5 > 2; //In valid – cannot assign boolean to int.
boolean flag = false;
if(flag)
{ }
if(flag = true)
{ }
int x = 5;
if(x = 0)
{ }
mohammed.sikander@cranessoftware.
com 29
30. Logical Operators
&& , || - Short-circuiting operators, Same as
C
& , | - evaluates both condition.
mohammed.sikander@cranessoftware.
com 30
if(++x > 5 & ++ y > 5)
{
}
Both x and y are updated
if(++x > 5 && ++ y > 5)
{
}
Only x is updated.
32. Bitwise Operators
Can be applied on integral types only
& , | , ^ , ~, >> , << , >>>
>>> (unsigned right shift)
If left and right are boolean, it is
relational.
(a > b & a > c)
If left and right are integral, it is
bitwise.
(a & c)
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com 32
33. To print in Binary Form
Integer.toBinaryString(int)
mohammed.sikander@cranessoftware.
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Output:
X = 23
10111
35. Control Flow - if
If (boolean)
◦ Condition should be of boolean
if( x ) invalid is not same as if(x != 0 ) (valid)
{ {
} }
boolean x = false;
if( x ) if(x = true )
{ {
} }
mohammed.sikander@cranessoftware.
com 35
37. Control Flow - switch
The switch statement is multiway branch
statement. It provides an easy way to
dispatch execution to different parts of your
code based on the value of an expression.
It often provides a better alternative than a
large series of if-else-if statements
Case label can be of
◦ Byte, short, char, int
◦ Enum , String (SE 7 & later)
◦ Character , Byte, Short,Integer(Wrapper class)
◦ Break is not a must after every case (similar to
C).
mohammed.sikander@cranessoftware.
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38. Control Flow - switch
public static void main(String [] args)
{
byte b = 1;
switch(b)
{
case 1 : System.out.println("Case 1");
case 2 :System.out.println("Case 2");
}
}
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com 38
39. Iteration Statements
While
Do-while
For
Enhanced for loop for accessing array
elements
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com 39
40. Enhanced for Loop
It was mainly designed for iteration
through collections and arrays. It can
be used to make your loops more
compact and easy to read.
int [ ] numbers = {5 , 8 , 2, 6,1};
For(int x : numbers)
◦ S.o.println(x);
mohammed.sikander@cranessoftware.
com 40
42. Enhanced For with
Multidimensional Arrays
int sum = 0;
int nums[][] = new int[3][5];
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);
mohammed.sikander@cranessoftware.
com 42
43. Method 2: No. of columns are same in all rows
Datatype [ ][ ] matrix;
Matrix = new datatype[row][col];
Method 3 : Each row can have diff. no of
elements(cols)
Datatype [ ][ ] matrix;
Matrix = new datatype[row][ ];
For(I = 0 ; I < row ; i++)
◦ Matrix[i] = new datatype[col]
mohammed.sikander@cranessoftware.
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44. break
Unlabelled break & continue – similar to c/c++
Labelled break
search:
for (i = 0; i < arrayOfInts.length; i++) {
for (j = 0; j < arrayOfInts[i].length; j++) {
if (arrayOfInts[i][j] == searchfor) {
foundIt = true;
break search;
}
}
} mohammed.sikander@cranessoftware.
com 44
46. Kangaroo
https://www.hackerrank.com/challenges/kangaroo
There are two kangaroos on an x-axis ready to jump in the
positive direction (i.e, toward positive infinity). The first
kangaroo starts at location x1 and moves at a rate
of v1 meters per jump. The second kangaroo starts at
location x2 and moves at a rate of v2 meters per jump.
Given the starting locations and movement rates for each
kangaroo, can you determine if they'll ever land at the
same location at the same time?
Input Format
A single line of four space-separated integers denoting the
respective values of x1, v1, x2, and v2.
Output Format
Print No if they cannot land on the same location at the same
time.
Print YES if they can land on the same location at the same
time; also print the location where they will land at same time.
Note: The two kangaroos must land at the same location after making the same
number of jumps.
mohammed.sikander@cranessoftware.
com 46
public class FirstProgram {
/**
* @param args
*/
public static void main(String[] args) {
System.out.println("My First Java Program");
}
}
How can we verify the size.
Ans : By checking the range of values
In Java SE 7 and later, any number of underscore characters (_) can appear anywhere between digits in a numerical literal. This feature enables you, for example. to separate groups of digits in numeric literals, which can improve the readability of your code.
long creditCardNumber = 1234_5678_9012_3456L;
long hexBytes = 0xFF_EC_DE_5E;
long hexWords = 0xCAFE_BABE; byte nybbles = 0b0010_0101;
long bytes = 0b11010010_01101001_10010100_10010010;
You can place underscores only between digits; you cannot place underscores in the following places:
At the beginning or end of a number
Adjacent to a decimal point in a floating point literal
Prior to an F or L suffix
In positions where a string of digits is expected
10.0+2.0/(3.0−2.0*2.0);
If(x) – x is integer
If(x != 0) result is boolean.
boolean flag = false;
if(flag) //Valid in Java
{ }
if(flag = true) //valid
{ }
int x = 5;
if(x = 0) //Invalid in Java
{
}
public static void main(String[] args) {
int a = 5;
int b = 10;
boolean res = a > b;
if(res)
System.out.println(a);
else
System.out.println(b);
}
