Syllabus (1)

Week Chapters

1 Introduction to the course, basic java language programming concepts:

Primitive Data Types and Operations

1, 2

2 Methods, Control Statements, Arrays 4, 3, 5

3 Object Oriented Programming: Objects and Classes 6

4 Data Member, Member Method, Static and final members. Constructor

6

5 Visibility Modifiers, Acessors, and Mutators 6

6 Inheritance, Object Class 8

7 Review + Array of Objects, Some handy Java Classes; Arrays, String, StringBuffer, StringTokenizer, Vector

7

8 MIDTERM

Methods, Control Statements, Arrays

Syllabus (2)9 Array of Objects, Some handy Java Classes; Arrays, String,

StringBuffer, StringTokenizer, Vector7

10 Concrete class, Abstract Class, Interface 9

11 Polymorphism 8

12 Error Handling, Exception Classes and Custom Java Exceptions

15

13 GUI Programming, event driven programming, components and containers, AWT (Abstract Window Toolkit), swing

11, 12, 13

14 GUI Programming, event driven programming, components and containers, AWT (Abstract Window Toolkit), swing

11, 12, 13

15 GUI Programming, Applet 14

16 Review

17 FINAL

Chapter 4 Methods Introducing Methods

– Benefits of methods, Declaring Methods, and Calling Methods

Passing Parameters– Pass by Value

Overloading Methods– Ambiguous Invocation

Scope of Local Variables Method Abstraction The Math Class Case Studies Recursion (Optional)

Introducing Methods

Method StructureA method is a collection of statements that are grouped together to perform an operation.

Introducing Methods, cont.•parameter profile refers to the type, order, and number of the parameters of a method.

•method signature is the combination of the method name and the parameter profiles.

•The parameters defined in the method header are known as formal parameters.

•When a method is invoked, its formal parameters are replaced by variables or data, which are referred to as actual parameters.

Declaring Methods

public static int max(int num1, int num2) {

if (num1 > num2) return num1; else return num2;}

Calling Methods

Example 4.1 Testing the max method

This program demonstrates calling a method max to return the largest of the int values

TestMaxTestMax Run

Calling Methods, cont.

public static void main(String[] args) { int i = 5; int j = 2; int k = max(i, j); System.out.println( "The maximum between " + i + " and " + j + " is " + k); }

public static int max(int num1, int num2) { int result; if (num1 > num2) result = num1; else result = num2; return result; }

pass the value of i pass the value of j

Calling Methods, cont.

The main method is invoked.

Space required for the main method k:

j: 2 i: 5

The max method is invoked.

Space required for the max method result: 5

num2: 2 num1: 5

The max method is finished and the return value is sent to k.

The main method is finished.

Stack is empty

Space required for the main method k:

j: 2 i: 5

Space required for the main method k: 5

j: 2 i: 5

CAUTION

A return statement is required for a nonvoid method. The following method is logically correct, but it has a compilation error, because the Java compiler thinks it possible that this method does not return any value. public static int xMethod(int n) { if (n > 0) return 1; else if (n == 0) return 0; else if (n < 0) return –1; }

To fix this problem, delete if (n<0) in the code.

Passing Parameterspublic static void nPrintln(String message, int n) { for (int i = 0; i < n; i++) System.out.println(message);}

Pass by Value

Example 4.2 Testing Pass by value

This program demonstrates passing values to the methods.

TestPassByValueTestPassByValue Run

Pass by Value, cont.

The main method is invoked

The values of num1 and num2 are passed to n1 and n2. Executing swap does not affect num1 and num2.

Space required for the main method

num2: 2 num1: 1

The swap method is invoked

Space required for the main method

num2: 2 num1: 1

Space required for the swap method temp:

n2: 2 n1: 1

The swap method is finished

Space required for the main method

num2: 2 num1: 1

The main method is finished

Stack is empty

Overloading Methods

Example 4.3 Overloading the max Method

public static double max(double num1, double num2) {

if (num1 > num2) return num1; else return num2;}

TestMethodOverloadingTestMethodOverloading Run

Ambiguous Invocation

Sometimes there may be two or more possible matches for an invocation of a method, but the compiler cannot determine the most specific match. This is referred to as ambiguous invocation. Ambiguous invocation is a compilation error.

Ambiguous Invocationpublic class AmbiguousOverloading { public static void main(String[] args) { System.out.println(max(1, 2)); }  public static double max(int num1, double num2) { if (num1 > num2) return num1; else return num2; } public static double max(double num1, int num2) { if (num1 > num2) return num1; else return num2; }}

Scope of Local Variables

A local variable: a variable defined inside a method.

Scope: the part of the program where the variable can be referenced.

The scope of a local variable starts from its declaration and continues to the end of the block that contains the variable. A local variable must be declared before it can be used.

Scope of Local Variables, cont.

You can declare a local variable with the same name multiple times in different non-nesting blocks in a method, but you cannot declare a local variable twice in nested blocks.

Scope of Local Variables, cont.

public static void method1() { int x = 1; int y = 1;

for (int i = 1; i < 10; i++) {

x += i; }

for (int i = 1; i < 10; i++) {

y += i; } }

It is fine to declare i in two non-nesting blocks

public static void method2() { int i = 1; int sum = 0;

for (int i = 1; i < 10; i++) {

sum += i; } }

It is wrong to declare i in two two nesting blocks

Scope of Local Variables, cont.// Fine with no errorspublic static void correctMethod() { int x = 1; int y = 1; // i is declared for (int i = 1; i < 10; i++) { x += i; } // i is declared again for (int i = 1; i < 10; i++) { y += i; }}

Scope of Local Variables, cont.

// With no errorspublic static void incorrectMethod() { int x = 1; int y = 1; for (int i = 1; i < 10; i++) { int x = 0; x += i; }}

Method Abstraction

You can think of the method body as a black box that contains the detailed implementation for the method.

Method Signature

Method body

Black Box

Optional Input Optional returnvalue

Benefits of Methods

• Write a method once and reuse it anywhere.

• Information hiding. Hide the implementation from the user.

• Reduce complexity.

The Math Class Class constants:

– PI– E

Class methods: – Trigonometric Methods – Exponent Methods– Rounding Methods– min, max, abs, and random Methods

Trigonometric Methods

sin(double a)

cos(double a)

tan(double a)

acos(double a)

asin(double a)

atan(double a)

Exponent Methods exp(double a)

Returns e raised to the power of a.

log(double a)

Returns the natural logarithm of a.

pow(double a, double b)

Returns a raised to the power of b.

sqrt(double a)

Returns the square root of a.

Rounding Methods double ceil(double x)

x rounded up to its nearest integer. This integer is returned as a double value.

double floor(double x)x is rounded down to its nearest integer. This integer is returned as a

double value.

double rint(double x)x is rounded to its nearest integer. If x is equally close to two integers,

the even one is returned as a double.

int round(float x)Return (int)Math.floor(x+0.5).

long round(double x)Return (long)Math.floor(x+0.5).

min, max, abs, and random

max(a, b)and min(a, b)Returns the maximum or minimum of two parameters.

abs(a)Returns the absolute value of the parameter.

random()Returns a random double valuein the range [0.0, 1.0).

Example 4.4 Computing Taxes with Methods

Example 3.1, “Computing Taxes,” uses if statements to check the filing status and computes the tax based on the filing status. Simplify Example 3.1 using methods. Each filing status has six brackets. The code for computing taxes is nearly same for each filing status except that each filing status has different bracket ranges. For example, the single filer status has six brackets [0, 6000], (6000, 27950], (27950, 67700], (67700, 141250], (141250, 307050], (307050, ), and the married file jointly status has six brackets [0, 12000], (12000, 46700], (46700, 112850], (112850, 171950], (171950, 307050], (307050, ).

Example 4.4 Computing Taxes with Methods

The first bracket of each filing status is taxed at 10%, the second 15%, the third 27%, the fourth 30%, the fifth 35%, and the sixth 38.6%. So you can write a method with the brackets as arguments to compute the tax for the filing status. The signature of the method is:public static double computeTax(double income, int r1, int r2, int r3, int r4, int r5)

ComputeTaxWithMethodComputeTaxWithMethod Run

Example 4.5 Computing Mean and Standard Deviation

Generate 10 random numbers and compute the mean and standard deviation

ComputeMeanDeviationComputeMeanDeviation Run

n

xmean

n

ii

1

1

)(

1

2

12

nn

xx

deviation

n

i

n

ii

i

Example 4.6 Obtaining Random Characters

Write the methods for generating random characters. The program uses these methods to generate 175 random characters between ‘!' and ‘~' and displays 25 characters per line. To find out the characters between ‘!' and ‘~', see Appendix B, “The ASCII Character Set.”

RandomCharacterRandomCharacter Run

Example 4.6 Obtaining Random Characters, cont.

Appendix B: ASCII Character Set

Case Studies

Example 4.7 Displaying Calendars

The program reads in the month and year and displays the calendar for a given month of the year.

PrintCalendarPrintCalendar Run

Design Diagram

printCalendar (main)

readInput printMonth

getStartDay printMonthTitle printMonthBody

getTotalNumOfDays

getNumOfDaysInMonth

getMonthName

isLeapYear

Recursion (Optional)

Example 4.8 Computing Factorial

factorial(0) = 1;factorial(n) = n*factorial(n-1);

Factorial(3) = 3 * factorial(2) = 3 * (2 * factorial(1)) = 3 * ( 2 * (1 * factorial(0))) =

3 * ( 2 * ( 1 * 1))) = 3 * ( 2 * 1) = 3 * 2 = 6

ComputeFactorialComputeFactorial Run

Example 4.8 Computing Factorial, cont.

factorial(4) = 4*factorial(3)

factorial(3) = 3*factorial(2)

factorial(2) = 2*factorial(1)

factorial(1) = 1*factorial(0)

Step 6: factorial(1) returns 1 (1*1)

main method: factorial(4)

Step 1: factorial(4) calls factorial(3)

factorial(4) is called in the main

Step 2: factorial(3) calls factorial(2)

Step 3: factorial(2) calls factorial(1)

factorial(0) = 1

Step 4: factorial(1) calls factorial(0)

Step 5: factorial(0) returns 1

Step 7: factorial(2) returns 2 (2*1)

Step 8: factorial(3) returns 6 (3*2)

Step 9: factorial(4) returns 24 (4*6)

Example 4.8 Computing Factorial, cont.

Space Requiredfor factorial(4)

1 Space Requiredfor factorial(4)

2 Space Requiredfor factorial(3)

Space Requiredfor factorial(4)

3

Space Requiredfor factorial(3)

Space Requiredfor factorial(2)

Space Requiredfor factorial(4)

4

Space Requiredfor factorial(3)

Space Requiredfor factorial(2)

Space Requiredfor factorial(1)

Space Requiredfor factorial(4)

5

Space Requiredfor factorial(3)

Space Requiredfor factorial(2)

Space Requiredfor factorial(1)

Space Requiredfor factorial(0)

Space Requiredfor factorial(4)

6

Space Requiredfor factorial(3)

Space Requiredfor factorial(2)

Space Requiredfor factorial(1)

Space Requiredfor factorial(4)

7

Space Requiredfor factorial(3)

Space Requiredfor factorial(2)

Space Requiredfor factorial(4)

8 Space Requiredfor factorial(3)

Space Requiredfor factorial(4)

9

Fibonacci Numbers

Example 4.8 Computing Finonacci Numbers0 1 1 2 3 5 8 13 21 34 55 89…

f0 f1

fib(0) = 0;

fib(1) = 1;

fib(n) = fib(n-1) + fib(n-2); n>=2

fib(3) = fib(2) + fib(1) = (fib(1) + fib(0)) + fib(1) = (1 + 0) +fib(1) = 1 + fib(1) = 1 + 1 = 2

Fibonacci Numbers, cont

ComputeFibonacciComputeFibonacci Run

Fibonnaci Numbers, cont.

fib(4)=

fib(3) + fib(2)

call fib(3)

1

fib(3)= fib(2) + fib(1)

2 return fib(3)

call fib(2)

fib(2)= fib(1) + fib(0)

3

return fib(2)

call fib(1)

fib(1)= 1

4

return fib(1)

fib(2)= fib(1) + fib(0)

7

fib(0)= 0

5

fib(1)= 1

6 fib(1)= 1

8

return fib(1)

fib(0)= 1

9

Towers of Hanoi

Example 4.10 Solving the Towers of Hanoi Problem

Solve the towers of Hanoi problem.

TowersOfHanoiTowersOfHanoi Run

Towers of Hanoi, cont.

A

A

B

C

Step 0: Starting status

C

B

Step 2: Move disk 2 from A to C

A B

Step 3: Move disk 1 from B to C

C

A B

Step 4: Move disk 3 from A to B

C

A B

Step 5: Move disk 1 from C to A

CA B

Step 1: Move disk 1 from A to B

C

A B

Step 7: Mve disk 1 from A to B

C

A B

Step 6: Move disk 2 from C to B

C

Exercise 4.11 GCDgcd(2, 3) = 1

gcd(2, 10) = 2

gcd(25, 35) = 5

gcd(205, 301) = 5

gcd(m, n)

Approach 1: Brute-force, start from min(n, m) down to 1, to check if a number is common divisor for both m and n, if so, it is the greatest common divisor.

Approach 2: Euclid’s algorithm

Approach 3: Recursive method

Approach 2: Euclid’s algorithm// Get absolute value of m and n;

t1 = Math.abs(m); t2 = Math.abs(n);

// r is the remainder of t1 divided by t2;

r = t1 % t2;

while (r != 0) {

t1 = t2;

t2 = r;

r = t1 % t2;

}

 

// When r is 0, t2 is the greatest common divisor between t1 and t2

return t2;

Approach 3: Recursive Method

gcd(m, n) = n if m % n = 0;gcd(m, n) = gcd(n, m % n); otherwise;

Chapter 3 Control StatementsSelection Statements

–Using if and if...else–Nested if Statements–Using switch Statements–Conditional Operator

Repetition Statements–Looping: while, do-while, and for–Nested loops–Using break and continue

Selection Statements

if Statements

switch Statements

Conditional Operators

if Statements

if (booleanExpression) { statement(s);}

Example:if (i > 0 && i < 10) { System.out.println("i is an " + "integer between 0 and 10");}

CautionAdding a semicolon at the end of an if clause is a common mistake.

if (radius >= 0);

{

area = radius*radius*PI;

System.out.println(

"The area for the circle of radius " +

radius + " is " + area);

}

This mistake is hard to find, because it is not a compilation error or a runtime error, it is a logic error.

This error often occurs when you use the next-line block style.

Wrong

The if...else Statement

if (booleanExpression) {

statement(s)-for-the-true-case;

}

else {

statement(s)-for-the-false-case;

}

if...else Example

if (radius >= 0) { area = radius * radius * 3.14159;

System.out.println("The area for the “ + “circle of radius " + radius + " is " + area);}else { System.out.println("Negative input");}

Multiple Alternative if Statementsif (score >= 90) grade = ‘A’;else if (score >= 80) grade = ‘B’; else if (score >= 70) grade = ‘C’; else if (score >= 60) grade = ‘D’; else grade = ‘F’;

if (score >= 90) grade = ‘A’;else if (score >= 80) grade = ‘B’;else if (score >= 70) grade = ‘C’;else if (score >= 60) grade = ‘D’;else grade = ‘F’;

NoteThe else clause matches the most recent if clause in the same block. For example, the following statement int i = 1; int j = 2; int k = 3; if (i > j) if (i > k) System.out.println("A"); else System.out.println("B");

is equivalent to int i = 1; int j = 2; int k = 3; if (i > j) if (i > k) System.out.println("A"); else System.out.println("B");

Note, cont.Nothing is printed from the preceding statement. To force the else clause to match the first if clause, you must add a pair of braces: int i = 1;

int j = 2;

int k = 3;

if (i > j) {

if (i > k)

System.out.println("A");

}

else

System.out.println("B");

This statement prints B.

Example 3.1 Computing TaxesThe US federal personal income tax is calculated based on the filing status and taxable income. There are four filing status: single filers, married filing jointly, married filing separately, and head of household. The tax rates for 2002 are shown in Table 3.1.

Example 3.1 Computing Taxes

Compute TaxCompute Tax Run

switch Statementsswitch (status) {

case 0: compute taxes for single filers;

break;

case 1: compute taxes for married file jointly;

break;

case 2: compute taxes for married file separately;

break;

case 3: compute taxes for head of household;

break;

default: System.out.println("Errors: invalid status");

System.exit(0);

}

switch Statement Flow Chart

status is 0 Compute tax for single filers break

Compute tax for married file jointly break status is 1

Compute tax for married file separatly break status is 2

Compute tax for head of household break status is 3

Default actions default

Next Statement

switch Statement RulesThe switch-expression must yield a value of char, byte, short, or int type and must always be enclosed in parentheses.

The value1, ..., and valueN must have the same data type as the value of the switch-expression. The resulting statements in the case statement are executed when the value in the case statement matches the value of the switch-expression. (The case statements are executed in sequential order.)

The keyword break is optional, but it should be used at the end of each case in order to terminate the remainder of the switch statement. If the break statement is not present, the next case statement will be executed.

switch Statement Rules, cont.

The default case, which is optional, can be used to perform actions when none of the specified cases is true.      The order of the cases (including the default case) does not matter. However, it is a good programming style to follow the logical sequence of the cases and place the default case at the end.

Conditional Operator

if (x > 0) y = 1else y = -1;

is equivalent to

y = (x > 0) ? 1 : -1;

Ternary operatorBinary operatorUnary operator

Conditional Operator

if (num % 2 == 0)

System.out.println(num + “is even”);else System.out.println(num + “is odd”);

System.out.println( (num % 2 == 0)? num + “is even” : num + “is odd”);

Conditional Operator, cont.

(booleanExp) ? exp1 : exp2

Repetitions

while Loops

do-while Loops for Loops

break and continue

while Loop Flow Chartwhile (continuation-condition) {

// loop-body;

}

while Loop Flow Chart, cont.

int i = 0;while (i < 100) { System.out.println( "Welcome to Java!"); i++;}

false

true

System.out.println("Welcoem to Java!"); i++;

Next Statement

(i < 100)

i = 0;

Example 3.2: Using while Loops

TestWhile.java

TestWhileTestWhile Run

CautionDon’t use floating-point values for equality checking in a loop control. Since floating-point values are approximations, using them could result in imprecise counter values and inaccurate results. This example uses int value for data. If a floating-point type value is used for data, (data != 0) may be true even though data is 0.

// data should be zerodouble data = Math.pow(Math.sqrt(2), 2) - 2; if (data == 0) System.out.println("data is zero");else System.out.println("data is not zero");

do-while Loop

false

true

Statement(s)

NextStatement

Continue condition?

do {

// Loop body;

} while (continuation-condition);

for Loopsfor (initial-action; loop-continuation-condition;

action-after-each-iteration) { //loop body;}

int i = 0;while (i < 100) { System.out.println("Welcome to Java!" + i); i++; }

Example:

int i;for (i = 0; i < 100; i++) { System.out.println("Welcome to Java!" + i); }

for Loop Flow Chartfor (initial-action; loop-continuation-condition; action-after-each-iteration) { //loop body;}

for Loop Example

i<100?

System.out.println( “Welcom to Java!”);

true

false i++

i = 0

Next Statement

int i;for (i = 0; i<100; i++) { System.out.println( "Welcome to Java");}

for Loop Examples

Examples for using the for loop:

Example 3.3: Using for Loops

TestSumTestSum

TestMulTableTestMulTable

Example 3.4: Using Nested for Loops

Run

Run

Which Loop to Use?The three forms of loop statements, while, do-while, and for, are expressively equivalent; that is, you can write a loop in any of these three forms.

I recommend that you use the one that is most intuitive and comfortable for you. In general, a for loop may be used if the number of repetitions is known, as, for example, when you need to print a message 100 times. A while loop may be used if the number of repetitions is not known, as in the case of reading the numbers until the input is 0. A do-while loop can be used to replace a while loop if the loop body has to be executed before testing the continuation condition.

Caution

Adding a semicolon at the end of the for clause before the loop body is a common mistake, as shown below:

for (int i=0; i<10; i++);

{

System.out.println("i is " + i);

}

Logic Error

Caution, cont.Similarly, the following loop is also wrong:int i=0; while (i < 10);{ System.out.println("i is " + i); i++;}

In the case of the do loop, the following semicolon is needed to end the loop.int i=0; do { System.out.println("i is " + i); i++;} while (i<10);

Logic Error

Correct

The break Keyword

The continue Keyword

Using break and continue

Examples for using the break and continue keywords:

Example 3.5: TestBreak.java

Example 3.6: TestContinue.java

TestBreakTestBreak

TestContinueTestContinue

Run

Run

Example 3.7 Finding the Sales Amount

You have just started a sales job in a department store. Your pay consists of a base salary and a commission. The base salary is $5,000. The scheme shown below is used to determine the commission rate.Sales Amount Commission Rate$0.01–$5,000 8 percent$5,000.01–$10,000 10 percent$10,000.01 and above 12 percent

Your goal is to earn $30,000 in a year. Write a program that will find out the minimum amount of sales you have to generate in order to make $30,000.

FindSalesAmountFindSalesAmount RunRun

Example 3.8 Displaying a Pyramid of Numbers

In this example, you will use nested loops to print the following output:

1 212 32123 4321234543212345

Your program prints five lines. Each line consists of three parts. The first part comprises the spaces before the numbers; the second part, the leading numbers, such as 3 2 1 on line 3; and the last part, the ending numbers, such as 2 3 on line 3.

PrintPyramidPrintPyramid RunRun

Example 3.9 Displaying Prime Numbers

This example displays the first 50 prime numbers in five lines, each of which contains 10 numbers. An integer greater than 1 is prime if its only positive divisor is 1 or itself. For example, 2, 3, 5, and 7 are prime numbers, but 4, 6, 8, and 9 are not.

The problem can be broken into the following tasks:•For number = 2, 3, 4, 5, 6, ..., test whether the number is prime.•Determine whether a given number is prime.•Count the prime numbers.•Print each prime number, and print 10 numbers per line.

PrimeNumberPrimeNumber RunRun