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Lesson3: JAVA
INTRODUCTION TO JAVA PROGRAMMING
Operators and Flow of Control
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Relational Operator
The Relational Operators determine therelationship that one operand has to theother.
e.g. Equality and OrderingOperator Result== Equal to
!= Not equal to
> Greater than
< Less than
>= Greater than or equal to
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Boolean Logical Operator
Boolean logical operators operate only on booleanoperands.Operator Result
& Logical AND
| Logical OR^ Logical XOR(exclusive OR)|| Short-Circuit OR&& Short-Circuit AND! Logical Unary NOT== Equal to!= Not Equal to
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Boolean Logical Operator
Logical Operation Effect
A B A|B A&B A^B !A
0 0 0 0 0 11 0 1 0 1 0
0 1 1 0 1 1
1 1 1 1 0 0
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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
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Flow of Control
Sequence
Selection
Iteration
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Sequence
Key points:
order of operations may or may not beimportant
order of evaluation within a singlestatement can be critical
example:a = b++;
a = b = read(input);
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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!)
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Selection
if (condition) {
statement1;
}else {
statement2;
}
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Selection
if (condition){
statement1; condition must
} be of type boolean
else {
statement2;}
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Selection
if (condition) {
statement1;
}else {
statement2;
} else branch is optional
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Selection
if (condition) {
statement1;
}
else {
statement2;
} braces may be
omitted if they onlycontain a single
statement
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Selection
if (condition)
statement;
Brackets around theCondition are
essential
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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!) humanreaders
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Example conditions
if ((i < j) && (eof != true)) .
if ((i < j) && !eof) .
if ((i < j) && !eof()) .
if ((n = input.read())== 0)
Dont use = when you mean ==
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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.");}
}}
l 2
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Example 2class 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.
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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;elseseason= Bogus Month;
System.out.println(October is in the +season +.);
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Practice Exercise Continue
Write a Java Programme which will tellwhether X (a variable) is Even or Odd.
Write a Java Programme which will specifywhether a birth year was in 1950s, 1960s,1970s, 1980s, 1990s.
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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.
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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 notSemiColon or Delimeter
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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;
}}
}
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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+.);
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Iteration
while simplest
for most common
do .. While uncommon
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While Statement
while ( condition)
{
body statements;
}
while the conditionevaluates to true,repeatedly loop executingthe body statements
condition is tested
before each passthrough the body
body statements should
have some effect on thecondition or you could
loop indefinitely
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While Statement
int a=10;
while (a > 0) {
System.out.println (a);a = a-1;
}
System.out.println (You Lost The Game");
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Practice While Statement
int a=10;while (a > 0) {
System.out.println (a);
while(a>0 && a
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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
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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
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do...while statement
int a=10;
do{
System.out.println (a);a = a-1;
} while (a > 0);
System.out.println (You Lost The Game");
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for statement
for (initialisation; while condition; end of loop operation) {
body statements;
}
for KeywordVariable Initialisation
Loop Condition
Loop termination Condition
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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
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for statement Difference and common features ofwhile and for loop
for (INITIALIZER; CONDITION; INCREMENTOR) {
BODY
}
INITIALIZER;
while (CONDITION) {
BODY
INCREMENTOR
}
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for statement
for (int i=0; i
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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
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Practice for statementint number;
boolean flag = true;
number = 4;
for(int i=2; i
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Nested for Loops Like any other programming Language Java does
allow loops
for(int i=0; i
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Extra Information on for Loops
you can nest loops
you can break execution and jump outside
the loop