Lesson3: JAVA
INTRODUCTION TO JAVA PROGRAMMING
Operators and Flow of Control
Relational Operator
•The Relational Operators determine the relationship that one operand has to the other.
e.g. Equality and Ordering
Operator Result
== Equal to
!= Not equal to
> Greater than
< Less than
>= Greater than or equal to
<= Less than or equal to
Boolean Logical Operator
• Boolean logical operators operate only on boolean operands.
Operator Result
& Logical AND
| Logical OR
^ Logical XOR(exclusive OR)
|| Short-Circuit OR
&& Short-Circuit AND
! Logical Unary NOT
== Equal to
!= Not Equal to
Boolean Logical Operator
• Logical Operation Effect
A B A|B A&B A^B !A
0 0 0 0 0 1
1 0 1 0 1 0
0 1 1 0 1 1
1 1 1 1 0 0
Boolean Logical Operator (Code)
class Logic{
public static void main (String Args[]){
boolean a = true;
boolean b = false;
boolean c = a | b;
boolean d = a & b;
boolean e = a ^ b;
boolean f = (!a & b) | (a & !b);
boolean g = !a;
System.out.println(" a=" + a);
System.out.println(" b=" + b);
System.out.println(" a|b=" + c);
System.out.println(" a&b=" + d);
System.out.println(" a^b=" + e);
System.out.println(" !a&b|a&!b=" + f);
System.out.println(" !a=" + g);
}
} // Code is From “The Complete Reference JAVA 2”, Herbert Schildt
Flow of Control
• Sequence
• Selection
• Iteration
Sequence
• Key points:
– order of operations may or may not be important
– order of evaluation within a single statement can be critical
• example:
a = b++;
a = b = read(input);
Order of precedence
• parentheses before operators
• then multiplication and division
• then addition and subtraction
• left to right for equal precedence ops
• RHS of an assignment before LHS
• if in doubt use brackets
• use brackets anyway (to clarify to other readers!)
Selection
if (condition) {
statement1;
} else {
statement2;
}
Selection
if (condition) {
statement1; condition must
} be of type boolean
else {
statement2;
}
Selection
if (condition) {
statement1;
} else {
statement2;
} else branch is optional
Selection
if (condition) {
statement1;
} else {
statement2;
} braces may be
omitted if they only contain a single
statement
Selection
if (condition) statement;
Brackets around the Condition are
essential
Selection
if (condition1) {
if (condition2) {
statement1;
} else {
statement2;
}
} else {
statement3;
}
• if statements can be nested
• indentation ignored by the compiler but helps (or can mislead!) human readers
Example conditions
if ((i < j) && (eof != true)) ….
if ((i < j) && !eof) ….
if ((i < j) && !eof()) ….
if ((n = input.read())== 0) …
Don’t use = when you mean ==
Example Program
class Larger {
public static void main(String[] args) { int x=20;
int y=20;
if(x >= y){
if (x==y){
System.out.println("x="+x+" and y="+y+ " are Equal");
} else {
System.out.println("Both are unequal");
}
System.out.println(x+" is the larger.");
} else {
System.out.println(y+" is the larger.");
}
} }
Example 2
class Largest {
public static void main(String[] args){
// Read three integers and print which is the larger.
SimpleInput keyboard = new SimpleInput();
System.out.println("Please type three integers.");
int x = keyboard.nextInt(), y = keyboard.nextInt(), z = keyboard.nextInt();
// A variable to hold the answer.
int largest;
if(x >= y){ // It must be either x or z.
if(x >= z){
largest = x;
} else{
largest = z;
} }
else{ // It must be either y or z.
if(y >= z){
largest = y;
} else{
largest = z;
} }
System.out.println("The largest is: "+largest);
}
} // Program Code is courtesy of David J. Barnes.
Practice Exercise
int month=10;
String season;
If (month==12 || month ==1 || month ==2) season =“Winter”;
else if(month==3 || month ==4 || month ==5) season=“Spring”;
else if(month==6 || month ==7 || month ==8) season=“Summer”;
else if(month==9 || month ==10 || month ==11) season=“Autumn”;
else
season= “Bogus Month”;
System.out.println(“October is in the ”+season +”.”);
Practice Exercise Continue
• Write a Java Programme which will tell whether X (a variable) is Even or Odd.
• Write a Java Programme which will specify whether a birth year was in 1950s, 1960s, 1970s, 1980s, 1990s.
Selection-switch
switch (Condition) {
Case 1:
Statement1;
Case 2:
Statement 2;
Break;
....
....
Default:
Statement n;
Break;
}
Condition should be int, short, byte or a char type
Switch Selection is
replacement of If-else for multiple selections and for multiple conditions.
Selection-switch
switch (Condition) {
Case 1:
Statement1;
Case 2:
Statement 2;
break;
....
....
default:
Statement n;
Break;
}
Break Used to break the condition
If none of the Case Statement satisfies Default condition will work
This Should be an Integer or Constant value
Remember this is COLON sign not
SemiColon or Delimeter
Example-switch Statement
class switchT{
public static void main(String[] Args) {
int x=1;
switch(x){
case 1:
System.out.println("Out put is 1: "+x);
case 2:
System.out.println("Out put is 2");
break;
case 3:
System.out.println("Out put is 3");
break;
default:
System.out.println("We were expecting X");
break;
} }
}
Practice Switch Statement
int month=10;
String season;
switch(month){
case 12:
case 1:
case 2:
season=“Winter”;
break;
}
System.out.println(“October is in the ”+ season+
“.”);
Iteration
• while simplest
• for most common
• do .. While uncommon
While Statement
while ( condition) {
body statements;
}
• while the condition evaluates to true,
repeatedly loop executing the body statements
• condition is tested before each pass through the body
• body statements should have some effect on the condition or you could loop indefinitely
While Statement
int a=10;
while (a > 0) {
System.out.println (a);
a = a-1;
}
System.out.println (“You Lost The Game");
Practice While Statement
int a=10;
while (a > 0) { System.out.println (a);
while(a>0 && a<5) {
System.out.println ("Inner Loop is working"+a);
a--;
}
a = a-1;
}
System.out.println ("You Lost The Game");
Practice While Statement
int n=10;
while (n != 1) {
System.out.println (n);
if (n%2 == 0) { // n is even n = n / 2;
}
else { // n is odd n = n*3 + 1;
} }
// Work Out Yourself to find the Output
do... while Statement
do {
body statements;
}
while ( condition);
• similar to while statement
• BUT condition is tested after each pass through the body
• so body statements will always be executed at least once
• body statements should have some effect on the
condition or you could loop indefinitely
do...while statement
int a=10;
do{
System.out.println (a);
a = a-1;
} while (a > 0);
System.out.println (“You Lost The Game");
for statement
for (initialisation; while condition; end of loop operation) {
body statements;
}
for Keyword Variable Initialisation Loop Condition
Loop termination Condition
for statement
• most convenient method for counter based iterations
• sequence of execution:
– initialisation
– is while condition true?
– if so, execute body statements – execute end of loop operation – is while condition true
etc
for statement
• Difference and common features of while and for loop for (INITIALIZER; CONDITION; INCREMENTOR) {
BODY
}
INITIALIZER;
while (CONDITION) { BODY
INCREMENTOR
}
for statement
for (int i=0; i<10; i++) { System.out.print(i + “ “);
}
output:
0 1 2 3 4 5 6 7 8 9
for statement
• break statement has importance in loop statements
• After reading break statement our compiler came out of loop and read the next statement after loop
Practice for statement
int number;
boolean flag = true;
number = 4;
for(int i=2; i<=number/2; i++) {
if( (number % i) == 0) {
flag = false;
break;
} }
if(flag)
System.out.println("This is Prime Number");
else
System.out.println("This is Not Prime Number");
Nested for Loops
• Like any other programming Language Java does allow loops
for(int i=0; i<3; i++) {
System.out.println(“i =”+i);
System.out.println();
for (int j=0; j<100; j++) { if(j==10) break;
System.out.println(“j =”+ j);
} System.out.println(); }
System.out.println(“Loops Completed”);
Extra Information on for Loops
• you can nest loops
• you can break execution and jump outside the loop
