2. Objective
On completion of this period you would be able to
know
• Various selection statements available in Java
2
3. Recap
• In the previous class we have discussed
• Various types of operators
3
4. Selection statements of Java
• Java language supports the following selection
statements
• If statement
• Switch statement
• Conditional operator statement
4
5. The if Statement
if ( <boolean expression> ) {
<then block>
} Boolean
Boolean
Expression
Expression
if ( testScore >= 95 ){
Then
Then System.out.println("You are a good student");
Block
Block }
5
6. Control Flow of if
testScore >=
true
testScore >=
95?
95?
System.out.println
System.out.println
false
("You are aagood student");
("You are good student");
6
7. The if-else Statement
if (testScore < 50) {
This statement is
This statement is
System. out. println ("You did not pass"); executed ififthe testScore
executed the testScore
is less than 50.
is less than 50.
} else {
This statement is
This statement is
System. out. println ("You did pass"); executed ififthe testScore
executed the testScore
is 50 or higher.
is 50 or higher.
}
7
8. Syntax for the if-else Statement
if ( <boolean expression> ) {
<then block>
} else {
Boolean
Boolean
<else block> } Expression
Expression
if (testScore < 50) {
System.out.println("You did not pass");
Then
Then
Block
Block
} else {
System.out.println("You did pass");
else Block
else Block
}
8
9. Control Flow
false true
testScore < 50 ??
testScore < 50
System.out.println
System.out.println
System.out.println
System.out.println ("You did not
("You did not
("You did pass");
("You did pass"); pass");
pass");
9
10. The Nested-if Statement
• The then and else block of an if statement can contain any
valid statements, including other if statements. An if
statement containing another if statement is called a
nested-if statement
if (testScore >= 50) {
if (studentAge < 10) {
System.out.println("You did a great job");
} else {
System.out.println("You did pass");
}
} else { //test score < 70
System.out.println("You did not pass");
}
10
11. Control Flow of Nested-if Statement
true inner if
false testScore >= 50 ??
testScore >= 50
System.out.println
System.out.println
false studentAge < 10
studentAge < 10
true
("You did not
("You did not ??
pass");
pass");
System.out.println
System.out.println
System.out.println
System.out.println ("You did aagreat
("You did great
("You did pass");
("You did pass"); job");
job");
11
12. Compound Statements
• You have to use braces if the <then> or <else>
block has multiple statements
if (testScore < 70)
{ Then Block
Then Block
messageBox.show("You did not pass");
messageBox.show("Try harder next time");
}
else
{ Else Block
Else Block
messageBox.show("You did pass");
messageBox.show("Keep up the good work");
} 12
14. if - else- if
if (score >= 85) {
System.out.println(”Grade is A");
Test Grad
} else { Score e
if (score >= 75) {
System.out.println(”Grade is B"); 85 ≤ score A
} else {
75 ≤ score < B
if (score >= 65) {
85
System.out.println(”Grade is C");
} else { 65 ≤ score < C
if (score >= 50) { 75
System.out.println(”Grade is D");
50 ≤ score < D
} else {
65
System.out.println(”Grade is N");
} score < N
} 50
}
}
14
15. if - else- if
if (score >= 85) { Test Grad
System.out.println(”Grade is A"); Score e
} else if (score >= 75) {
85 ≤ score A
System.out.println(”Grade is B");
75 ≤ score < B
} else if (score >= 65) { 85
System.out.println(”Grade is C"); 65 ≤ score < C
} else if (score >= 50) { 75
System.out.println(”Grade is D"); 50 ≤ score < D
} else { 65
System.out.println(”Grade is N"); score < N
50
}
15
16. Matching else
if (x < y)
if (x < z)
System.out.println("Hello");
else
System.out.println("Good bye");
really means
if (x < y) {
if (x < z) {
System.out.println("Hello");
} else {
System.out.println("Good bye");
}
} 16
17. Matching else
if (x < y) {
if (x < z)
System.out.println("Hello");
} else {
System.out.println("Good bye");
}
means
if (x < y) {
if (x < z) {
System.out.println("Hello");
}
} else {
System.out.println("Good bye");
17
}
18. Syntax for the switch Statement
switch ( <arithmetic expression> ) {
<case label 1> : <case body 1>
…
<case label n> : <case body n>
}
Arithmetic Expression
Arithmetic Expression
switch ( fanSpeed ) {
case 1:
Case
Case
Label System.out.println("That's low");
Label
break;
case 2:
System.out.println("That's medium"); Case
Case
break; Body
Body
case 3:
System.out.println("That's high");
break;
}
18
19. The switch Statement
char standing;
System.out.println("(F)reshman, (S)ophmore, (J)unior, s(E)nior : ");
standing = SavitchIn.readLineNonwhiteChar();
switch (standing) {
case 'F': This statement
This statement
is executed ifif
is executed
System.out.println("Go to the Wellness Center");
the standing is
the standing is
break; equal to 'F'.
equal to 'F'.
case 'S':
System.out.println("Go to the Cox Building");
break;
case 'J':
System.out.println("Go to Ashe");
break;
case 'E': This statement
This statement
is executed ifif
is executed
System.out.println("Work it out yourself"); the standing is
the standing is
break; equal to 'E'.
equal to 'E'.
19
}
20. switch With break Statements
true
N ==
N ==
switch ( N ) { 11?? xx= 10;
= 10;
case 1: x = 10;
false break;
break;
break; true
N ==
N ==
case 2: x = 20; 22?? xx= 20;
= 20;
break;
false break;
break;
case 3: x = 30; true
N ==
N ==
break; 33?? xx= 30;
= 30;
}
false break;
break;
20
21. The switch Statement with default
switch ( <arithmetic expression> ) {
<case label 1> : <case body 1>
…
<case label n> : <case body n>
default: <default body>
}
switch ( binaryDigit ) {
case 0:
System.out.println("zero");
break;
case 1:
System.out.println("one");
break;
default:
System.out.println("That's not a binary digit");
break;
21
}
22. Switch With No break Statements
true
N ==
N == xx= 10;
switch ( N ) { 11?? = 10;
case 1: x = 10; false
case 2: x = 20; true
N ==
N == xx= 20;
case 3: x = 30; 22?? = 20;
} false
true
N ==
N == xx= 30;
= 30;
33??
false
22
23. Summary
• In this class we have discussed about various
selection statements
23
24. Assignment
• Write a Java program to find whether the given
year is leap or not
• Write a Java program to find the largest of three
numbers
• Write a Java program illustrating the functioning
of switch statement
24
25. Quiz
1.The only relational operation that can be
checked in switch
a) less than
b) greater than
c) equality
d) all of the above
25
26. Quiz
2.Which of the following control statement requires
break
a) If
b) If else
c) Switch
d) All of the above
26
29. Frequently Asked Questions
• Differentiate between switch and if else
statements
• List the various selection statements of Java
• Explain the various selection statements
29
30. swings
Struts
jdbc
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home
java previous question papers
OCT/NOV-2012 QUESTION PAPER
April / May 2012 c-09
October/ November-2011 c-09
April/ May 2011 c-09
April/ May 2011 c-05
Home 30
Hinweis der Redaktion
Chapter 6 -
Chapter 6 - Notice that the if–then statement is not necessary, because we can write any if–then statement using if–then–else by including no statement in the else block. For instance, the sample if–then statement can be written as if (testScore >= 95) { messageBox.show("You are an honor student"); } else { } In this book, we use if-then statements whenever appropriate.
Chapter 6 -
Chapter 6 -
Chapter 6 -
Chapter 6 -
Chapter 6 - It is possible to write if tests in different ways to achieve the same result. For example, the above code can also be expressed as if (testScore >= 70 && studentAge < 10) { messageBox.show("You did a great job"); } else { //either testScore < 70 OR studentAge >= 10 if (testScore >= 70) { messageBox.show("You did pass"); } else { messageBox.show("You did not pass"); } }
Chapter 6 -
Chapter 6 - Rules for writing the then and else blocks: - Left and right braces are necessary to surround the statements if the then or else block contains multiple statements. - Braces are not necessary if the then or else block contains only one statement. - A semicolon is not necessary after a right brace.
Chapter 6 - In this book, we will use Style 1, mainly because this style is more common among programmers. If you prefer Style 2, then go ahead and use it. Whichever style you choose, be consistent, because consistent look and feel are very important to make your code readable.
Chapter 6 - If we follow the general rule, the above if-else if will be written as below, but the style shown in the slide is the standard notation. if (score >= 90) messageBox.show("Your grade is A"); else if (score >= 80) messageBox.show("Your grade is B"); else if (score >= 70) messageBox.show("Your grade is C"); else if (score >= 60) messageBox.show("Your grade is D"); else messageBox.show("Your grade is F");
Chapter 6 - If we follow the general rule, the above if-else if will be written as below, but the style shown in the slide is the standard notation. if (score >= 90) messageBox.show("Your grade is A"); else if (score >= 80) messageBox.show("Your grade is B"); else if (score >= 70) messageBox.show("Your grade is C"); else if (score >= 60) messageBox.show("Your grade is D"); else messageBox.show("Your grade is F");
Chapter 6 - If you want the else to match with the first if , then you have to write if (x < y) { if (x < z) messageBox.show("Hello"); } else messageBox.show("Good bye");
Chapter 6 - If you want the else to match with the first if , then you have to write if (x < y) { if (x < z) messageBox.show("Hello"); } else messageBox.show("Good bye");
