Java Programming: Variables, Control Structures, and Arrays, Lecture notes of Java Programming

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Introduction to java

 How are Java programs written?

 How are variables declared?

 What are naming conventions in java?

 How are expressions specified?

 How are control structures defined?

 Conditional structure(if/else)

 Iteration structures (loops)

 The selective structure(switch)

Public keyword

 Public is a keyword

 Keywords :reserved words which have specific

meaning relevant to a compiler in java

programming language

 Public keyword indicates the following :

-- It is used as an access control modifier.

-- It is applicable to a class or a method.

-- public class, method or a variable are

visible to all the classes defined in different

package.

public class HelloWorld

Main

 public static void main (String[] args)

1. public - declares that the main method is publicly

accessible to other classes

 2. static - declares that the main method can be

invoked without creating an instance of the class

 3. void - declares that the main method does not return

any value.

 4. main - defines the name of the method 5. String[]

args - defines a parameter to the main method which

will contain any command line options passed by the

user when invoking the progam. These command line

options will be passed to the program as an array of

string objects.

Variables Declaration

 int myInt; /* Declaring an uninitialized

variable called 'myInt', of type 'int' */

 myInt = 35; // Initializing the variable

 int myInt = 35; // Declaring and initializing

the variable at the same time

 int a, b; // Declaring multiple variable of the

same type

 int a = 2, b = 3; // Declaring and initializing

multiple variables of the same type

Example : Fibonacci Series

Fibonacci:

class Fibonacci {

public static void main(String[] arg) {

int lo = 1;

int hi = 1;

System.out.println(lo);

while (hi < 50) {

System.out.println(hi);

hi = lo + hi;

lo = hi – lo;

}

}

}

8

Arrays in Java

 Declaration:

 int[] array_name; //declares an array of integers

String[] names; //declares an array of string

int[][] matrix; //this is an array of arrays(2d array)

 Memory Allocation:

 int[] num= {100, 200, 300, 400, 500, 600};

lengthOfArray= num.length;

 int[] array_name = new int[5]; // array of

integers of size 5

Arrays

Similarly, you can declare arrays of other types:

 byte[] anArrayOfBytes;

 short[] anArrayOfShorts;

 long[] anArrayOfLongs;

 float[] anArrayOfFloats;

 double[] anArrayOfDoubles;

 boolean[] anArrayOfBooleans;

 char[] anArrayOfChars;

 String[] anArrayOfStrings;

Switch

 class SwitchDemo {

 public static void main(String[] args)

 { int month = 8;

 switch (month)

 { case 1: System.out.println("January"); break;

 case 2: System.out.println("February"); break;

 case 3: System.out.println("March"); break;

 case 4: System.out.println("April"); break;

 case 5: System.out.println("May"); break;

 case 6: System.out.println("June"); break;

 case 7: System.out.println("July"); break;

 case 8: System.out.println("August"); break;

 case 9: System.out.println("September"); break;

 case 10: System.out.println("October"); break;

 case 11: System.out.println("November"); break;

 case 12: System.out.println("December"); break;

 default: System.out.println("Invalid month.");break; }

 OUTPUT: In this case, "August" is printed to standard output.

When to use switch and when

if/else….??

 …

Operators

 Assignment Operator: int cadence = 0;

 The Arithmetic Operators

 + additive operator (also used for String

concatenation)

 - subtraction operator

 * multiplication operator

 / division operator

 % remainder operator

Example Arithmetic operators

 class ArithmeticDemo {

 public static void main (String[] args){

 int result = 1 + 2; // result is now 3 System.out.println(result);

 result = result - 1; // result is now 2 System.out.println(result);

 result = result * 2; // result is now 4 System.out.println(result);

 result = result / 2; // result is now 2 System.out.println(result);

 result = result + 8; // result is now 10

 result = result % 7; // result is now 3

 System.out.println(result); } }

 You can also combine the arithmetic operators with the simple assignment operator to create compound assignments. For example,

 x+=1; and

 x=x+1; both increment the value of x by 1.

The Unary Operators

 The unary operators require only one operand; they

perform various operations such as

incrementing/decrementing a value by one, negating

an expression, or inverting the value of a boolean.

 + Unary plus operator; indicates positive value

(numbers are positive without this, however)

 - Unary minus operator; negates an expression

 ++ Increment operator; increments a value by 1

 -- Decrement operator; decrements a value by 1

! Logical complement operator; inverts the value of a

boolean

Unary Operator Example

 class UnaryDemo {

 public static void main(String[] args){

 int result = +1; // result is now 1

 System.out.println(result);

 result--; // result is now 0

 System.out.println(result);

 result++; // result is now 1

 System.out.println(result);

 result = -result; // result is now -

System.out.println(result);

 boolean success = false;

 System.out.println(success); // false

 System.out.println(!success); // true } }