COMP 110:Introduction to Programming

Tyler JohnsonApr 27, 2009

MWF 11:00AM-12:15PMSitterson 014

COMP 110: Spring 20092

Announcements

Final exam Monday May 4, 12 noonIn this room

Program 5 due today by 5pm

COMP 110: Spring 20093

Questions?

COMP 110: Spring 20094

Final Exam

20% of final grade

Exam will be cumulativeLecturesReadings from textbookLabsProgramsMidterm

No computers, notes, calculators etc.

You will be allowed a 1-page cheat-sheet

COMP 110: Spring 20095

Today in COMP 110

Review for Final

COMP 110: Spring 20096

Objects/Arrays & Memory

The value of an object is a memory address

Student s1 = new Student("Jack Smith", 2342342);Student s2 = new Student("Jack Smith", 2342342);

s1 == s2 is false!

Arrays are objects!

COMP 110: Spring 20097

What is the Output?

int a = 7;int b = a; b = 8;

System.out.println("A: " + a);System.out.println("B: " + b);

A: 7

B: 8

Output

//a is not changed by this

COMP 110: Spring 20098

What is the Output?

int[] a = {4, 5, 6};int[] b = a;b[0] = 3;

System.out.println("a: {" + a[0] + ", " + a[1] + ", " + a[2] + "}");

System.out.println("b: {" + b[0] + ", " + b[1] + ", " + b[2] + "}");

a: {3, 5, 6}

b: {3, 5, 6}

Output

//b holds same memory address as a//we’re changing both b & a!

This is like giving the array two names (a & b)

COMP 110: Spring 20099

Array Assignment

int[] a = {4, 5, 6};int[] b = a;b[0] = 3;

4 5 6a

b

3

COMP 110: Spring 200910

Copying Arrays

int[] a = {4, 5, 6};int[] b = new int[a.length]; //create a new array b

//copy a’s entries into bfor(int i = 0; i < b.length; b++) {

b[i] = a[i];}

COMP 110: Spring 200911

What is the Output?

public void changeNumber(int num) {num = 7;

}

public static void main(String[] args) {int a = 9;changeNumber(a);System.out.println("a = " + a);

int num = 9;changeNumber(num);System.out.println("num = " + num);

}

a = 9

num = 9

Output

COMP 110: Spring 200912

What is the Output?

public void changeNumber(int num) {num = 7;

}

public static void main(String[] args) {int[] a = {4, 5, 6};

changeNumber(a[0]);System.out.println("a: {" + a[0] + ", " + a[1] + ", " + a[2] + "}");

}

a: {4, 5, 6}

Output

COMP 110: Spring 200913

What is the Output?

public void changeArray(int[] array) {array[0] = 7;

}

public static void main(String[] args) {int[] a = {4, 5, 6};

changeArray(a);System.out.println("a: {" + a[0] + ", " + a[1] + ", " + a[2] + "}");

}

a: {7, 5, 6}

Output

COMP 110: Spring 200914

What is the Output?

public void changeArray(int[] array) {array = new int[3];array[0] = 7;array[1] = 5;array[2] = 6;

}

public static void main(String[] args) {int[] a = {4, 5, 6};

changeArray(a);System.out.println("a: {" + a[0] + ", " + a[1] + ", " + a[2] + "}");

}

a: {4, 5, 6}

Output

COMP 110: Spring 200915

Graphical Example

public void changeArray(int[] array) {array = new int[3];array[0] = 7;array[1] = 5;array[2] = 6;

}

public static void main(String[] args) {int[] a = {4, 5, 6};

changeArray(a);System.out.println("a: {" + a[0] + ", " + a[1] + ", " + a[2] + "}");

}

4 5 6a

array 7 5 6

a: {4, 5, 6}

Output

COMP 110: Spring 200916

Review Worksheet

COMP 110: Spring 200917

Course Evaluation