1. Branching Statement Condition Statement Condition list 1 listF F
Statement
list 2
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2. The Syntax of if and if-else statements
A Boolean expression (logical expression). In Java, there are two possible values: true and false.
if ( condition ) {
statement list; }
Reserved words
A reserved word can’t be used as an identifier
if ( condition ) {
statement list1; }
else
statement list2;
Indentation indicates that the statements in the statement list are at the level next to the if-else statement.
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3. Nested if/else statement
if ( condition 1 ) {
if ( condition 2 )
statement list; }
else };
Indentation indicates the level of statements.
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4. while Statement Condition list while (Condition) { Statement list }F
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5. Disney Ride in Program – OK
, but not really
Disney Ride in Program – OK
n = Integer.parseInt(
JOptionPane.showInputDialog(“How tall is the kid?”));
// IsBoy = true or false;
if (h < 4)
if (IsBoy)// Same as if (IsBoy == true)
System.out.println(“Take a Mickey”);
else
System.out.println(“Take a Mini.”);
System.out.println(“You can ride!!”);
System.out.println(“Go to the next stop.”);
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6. Ambiguity I saw the little girl with a binocular on the mountain top.
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7. Rule: else belongs to the nearest if that not yet has an else
if (condition1)
if (condition2) {
.....; }
else // not a kid
Indentation can’t help compiler
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8. Boy Scout: Is a kid? Parent? Is a boy? Give a guidebook Give a badge
Yes
Is a kid? No
Parent?
Is a boy? No No
Yes
Yes
Give a guidebook
Give a badge
Welcome
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9. Boy Scout: in program if (IsKid) { if (IsBoy)
System.out.println(“Take a Badge”); }
else // not a kid
if (IsParent)
System.out.println(“Take a Guidebook”);
System.out.println(“Welcome, everybody!.”);
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10. Boy Scout: wrong program
if (IsKid)
if (IsBoy)
System.out.println(“Take a Badge”);
else // not a kid
if (IsParent)
System.out.println(“Take a Guidebook”);
System.out.println(“Welcome, everybody!.”);
if (IsKid) {
if (IsBoy)
System.out.println(“Take a Badge”); }
else // not a boy
if (IsParent)
System.out.println(“Take a Guidebook”);
System.out.println(“Welcome, everybody!.”);
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11. Other forms of Nested if/else statements (Cascaded) I
if (condition_1)
statement_1;
if (condition_2)
statement_2;
if (condition_3)
statement_3;
if (condition_4)
statement_4;
if (condition_5)
statement_5;
if (condition_1)
statement_1;
else if (condition_2)
statement_2;
else if (condition_3)
statement_3;
else if (condition_4)
statement_4;
else if (condition_5)
statement_5;
V.S.
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12. Another form of Nested if/else statement (Cascaded)
if (points >= 640)
System.out.println(“A”);
else if (points >= 500)
System.out.println(“B”);
else if (points >= 400)
System.out.println(“C”);
else if (points >= 300)
System.out.println(“D”);
else
System.out.println(“F”);
Points
Grade
650 -- A B C D
0--299 F
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13. Other forms of Nested if/else statements (Cascaded) II
Logical and
if (condition_1)
if (condition_2)
if (condition_3)
if (condition_4)
statement_1;
else
statement_2;
if ( condition_1 &&
condition_2 &&
condition_3 &&
condition_4 )
statement_1;
else
statement_2; =
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14. Switch vs. Cascaded if/else
if (i == 1)
statement_1;
else if (i == 2)
statement_2;
else if (i == 3)
statement_3;
else if (i == 4)
statement_4;
else if (i == 5)
statement_5;
else if (i == 6)
statement_6;
switch (i) {
case 1: statement_1;
break;
case 2: statement_2;
case 3: statement_3;
case 4: statement_4;
case 5: statement_5;
case 6: statement_6; }
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15. == > < <= >= !=
Operators
Arithmetic operators:
/ * %
Relational operators:
== > < <= >= !=
Logical operators:
|| && !
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16. Logical Operators || && ! Assume x = 10 false true true false
|| && !
Assume x = 10
((18 <= x) && (x <= 50))
((18 <= x) || (x <= 50))
!(x < 5) is same as (x >= 5)
(((x % 2) == 0) && ((x % 3) == 0))
false
true
true
false
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17. De Morgan’s law !(A && B) is same as !A || !B
I am not a female student.
 I am not female or I am not a student.
I will not be in my office or in the lab.
 I will not be in my office and will not be in the lab.
!(A && B) is same as !A || !B
!(A || B) is same as !A && !B
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18. Extend City to a special one
import becker.robots.*;
public class City1 extends City {
public City1 () {
super();
new Wall(this,1,2,Direction.EAST);
new Wall(this,1,2,Direction.WEST);
new Wall(,1,2,Direction.NORTH);
TriangleRobot mark = new
TriangleRobot(this,0,0,Direction.NORTH);
mark.drawTriangle(11, 4, 7); }
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19. Extend City to a special one that takes parameters
import becker.robots.*;
public class TriangleCity extends City {
public TriangleCity (int strNo, int aveNo, int height) {
super();
new Wall(this,1,2,Direction.EAST);
new Wall(this,1,2,Direction.WEST);
new Wall(,1,2,Direction.NORTH);
TriangleRobot mark = new
TriangleRobot(this,0,0,Direction.NORTH);
mark.drawTriangle(strNo, aveNo, height); }
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20. What kind of actions (services) do we need?1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11
TriangleRobot mark = new
TriangleRobot(ny,0,0,Direction.NORTH);
mark.drawTriangle(11, 4, 7);
What kind of actions (services) do we need?
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21. The TriangleRobot needs to:
Know how to move to the right position (the left corner of the base).
Know how many things to put in one street (base).
Know how to move up
Know how to turn to the right direction
Know how to reduce the base for an upper street
Know when to stop
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22. The Robot needs to detect the environment+
public #
protected -
private
Robot
- int street
- int avenue
- Direction direction
- ThingBag backbag
+ Robot(City aCity, int aStreet, int anAvenue, Direction aDir)
+ void move()
+ void turnLeft()
+ void pickThing()
+ void putThing()
+ boolean canPickThing()
+ int countThingsInBackpack()
+ boolean frontIsClear()
+ int getAvenue()
+ Direction getDirection()
+ String getLabel()
+ double getSpeed()
+ int getStreet()
Accesors
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23. Definite Loop In programming a definite loop is more welcome.
I.e., number of iterations is known before the loop begins, at least the upper bound is known.
I.e., repeat the loop 100 times.
Precisely speaking, there is no definite loop in Java
We will talk about it in Chapter 5
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24. while loop for loop Statement Condition Statement list list
repeat n times
Statement
list
< n F
= n
while (Condition) {
Statement list }
for (???;???;???) {
Statement list }
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25. The general format for a for loop
for (Initialization_action; Condition; Condition_update) {
statement_list; } 1 2 3
Summation (n-1)+(n+1)
int i, n, sum = 0;
n = Integer.parseInt(
JOptionPane.showInputDialog(“input n”));
for (i=0; i<=n; i++) {
sum = sum + i; }
System.out.println(“This answer is ” + sum);
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26. Factorial of n is n(n-1)(n-2)...21
for (Initialization_action; Condition; Condition_update) {
statement_list; } 1 2 3
Factorial of n is n(n-1)(n-2)...21
int n,f=1;
n = Integer.parseInt(
JOptionPane.showInputDialog(“input n”) );
if (n < 0) System.out.println(“No can do!!”);
else
for (i=2; i<=n; i++) {
f = f*i; }
System.out.println(“This answer is ” + f);
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27. Compare for and while int i; i=2; for (i=2; i<=n; i++){
f *= i; }
i=2;
while (i<=n) {
f *= i;
i++; }
int i;
for (i=0; i<n; i++) {
.... }
i=0;
while (i<n) {
....
i++; }
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28. A special scope for the index variable of the for loop
for (int i=0; i<n; i++) {
.... }
scope
int i
scope
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