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Web & Systems Developer, 30 credits
Software development, part 2
2017-05-09
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Selection (if statement)
if (selection)
expression
selection
true
fals
expression
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Selection (if else statement)
import java.util.Scanner;
public class IfStatement{
public static void main (String [] args) {
Scanner scan = new Scanner (System.in);
double hourlySalary = 100;
int hours;
double payment;
System.out.print ("Enter the weekly hours worked:");
hours = scan.nextInt();
if (hours > 40) {
payment = 40 * hourlySalary + (hours - 40) * (hourlySalary * 1.5);
}
else {
payment = hours * hourlySalary;
}
System.out.println ("Weekly salary:" + payment + ” SEK");
}
}
Enter the weekly hours worked:60
Weekly salary: 7000.0 SEK
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Selection (if else statement)
import java.util.Scanner;
public class IfStatement2{
public static void main(String[] args){
Scanner scan = new Scanner(System.in);
int score;
int ratings;
System.out.print("Enter your exam result (0 to 100 points):");
score = scan.nextInt();
ratings = score / 10;
if (ratings > 7){
System.out.println("Your rate is: VERY GOOD");
}
else if (ratings < 5){
System.out.println("Your rate is: FAIL");
}
else{
System.out.println("Your rate is: GOOD");
}
}
Enter your exam result (0 to 100 points):65
Your rate is: GOOD
}
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Logical expressions
The logical NOT - expression:
!a
s true if a is false and false if a is true
The logical AND - expression:
a && b
is true if both a and b are true. otherwise false
The logical OR- expression:
a || b
is true if a or b or both are true. otherwise false
System.out.print ("Enter your rate:");
int result = scan.nextInt ();
if (result > 0 && result < 10) {
if (result > 4 && result < 8 ) {
System.out.println ("Result = G");
}
else if (result> 7) {
…
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Boolean expressions
A conditional statement often uses one of Java's relational operators, which all return boolean answer (true
or false):
== Equal to
!= Not equal
< Less than
> Greater than
<= Less than or equal to
>= Greater than or equal to
Note the difference between "equals" -operator (==) and the assignment operator (=)
System.out.print ("Enter your rate:");
int result = scan.nextInt ();
if (result >= 1 && result <= 10) {
if (result >= 5 && result <= 7 ) {
System.out.println ("Result = G");
}
else if (result> 7) {
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Boolska uttryck
2017-05-09
56 == 56
true
’a’ == ’a’
true
’a’ == ’A’
false
’x’ != ’z’
true
45 < 80
true
2 >= 6
false
2 >= 2
true
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Blockstatement
import java.util.Scanner;
public class Guess{
public static void main (String [] args) {
Scanner scan = new Scanner (System.in);
int rightNumber = 4;
int guessedNumber;
System.out.print ("Guess a number between 1 and 10:");
guessedNumber = scan.nextInt();
if (rightNumber == guessedNumber)
System.out.println ("GOOD, RIGHT NUMBER !!!");
else {
System.out.println ("Your answer was wrong.");
System.out.println ("The correct number was:" + rightNumber);
Block
}
}
}
Guess a number between 1 and 10: 6
Your answer was wrong.
The correct number was:4
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Nested statements
import java.util.Scanner;
public class IfStatement3 {
public static void main (String [] args) {
Scanner scan = new Scanner (System.in);
int result;
System.out.print ("Enter your rate:");
result = scan.nextInt ();
if (result> 0 && result <10) {
if (result> 4 && result <= 7) {
System.out.println ("Result =
}
else if (result> 7) {
System.out.println ("Result =
}
else {
System.out.println ("Result =
}
}
else {
System.out.println("You have entered an
}
}
}
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G");
VG");
U");
incorrect value!");
Enter your rate: 11
You have entered an incorrect value!
Magnus Wärja
Exercises
3.1 Selection
What is the result when you execute
public static void main (String[] args){
int x = 5;
int y = 10;
if (x > y)
System.out.println (x + ” is greater ");
else if (x < y)
System.out.println (y + " is greater");
else
System.out.println ("The numbers are equal");
}
3.1 Selection
What is the result when you execute
public static void main (String[] args){
int x = 5;
int y = 10;
if (x == y)
System.out.println ("The numbers are equal");
else
System.out.println ("The numbers are not equal");
}
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Exercises
3.3 Selection
What is the result when you execute
public static void main (String[] args){
int x = 5;
int y = 10;
if (x != y)
System.out.println ("The numbers are not equal");
else
System.out.println ("The numbers are equal");
}
3.4 Selection
What is the result when you execute
public static void main (String[] args){
int x = 5;
int y = 10;
if (x == 6 && y == 10)
System.out.println ("x = 6 andy = 10");
else if (x==6 || y==10)
System.out.println ("Either is x = 6 or y = 10");
else
System.out.println ("x is not 6 and y is not 10");
}
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Exercises
3.5 Selection
What is the result when you execute
public static void main (String[] args){
int resultat = 7;
if (resultat >= 9)
System.out.println ("Excellent");
if (resultat >= 8)
System.out.println (”Excellent");
if (resultat >= 7)
System.out.println (”Excellent");
if (resultat >= 6)
System.out.println (”Past");
if (resultat >= 5)
System.out.println (”Past");
if (resultat < 5)
System.out.println (”Fail");
}
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Exercises
3.6 Selection
What is the result when you execute
public static void main (String[] args){
int num = 80;
int max = 25;
if (num == 80 && max != 25)
System.out.println (”Apple");
System.out.println ("Pear");
System.out.println ("Banana");
}
Pear
Banana
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Exercises
3.7 Selection
Write a program that computes the following, depending on the age of the person:
Years left to retirement
Number of years the person has been retired
If the person has been retired this year
You can assume that the retirement age is 65 years.
Below are three examples of what your program should return depending on input value:
Example 1
Enter your age: 45
You retire if: 20 years
Example 2.
Enter your age: 75
You have been retired in: 10 years
Example 3.
Enter your age: 65
Congratulations, you were retired in the year !!!
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Exercises
3.8 Selection
Write a program that takes two integers and prints out the largest number
Below are three examples of what your program should return depending on input value:
Example 1
Enter the first number: 40
Enter the second number: 62
62 is greater than 40
Example 2
Enter the first number: 88
Enter the second number: 53
88 is greater than 53
Example 3
Enter the first number: 10
Enter the second number: 10
The numbers are equal
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Exercises
3.7 Selection
Write a program that computes the following, depending on the age of the person:
Years left to retirement
Number of years the person has been retired
If the person has been retired this year
You can assume that the retirement age is 65 years.
Below are three examples of what your program should return depending on input value:
Example 1
Enter your age: 45
You retire if: 20 years
Example 2.
Enter your age: 75
You have been retired in: 10 years
Example 3.
Enter your age: 65
Congratulations, you were retired in the year !!!
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Exercises
4.1 Iteration
Write a program that computes the following, depending on the age of the person:
Years left to retirement
Number of years the person has been retired
If the person has been retired this year
You can assume that the retirement age is 65 years.
Below are three examples of what your program should return depending on input value:
Example 1
Enter your age: 45
You retire if: 20 years
Example 2.
Enter your age: 75
You have been retired in: 10 years
Example 3.
Enter your age: 65
Congratulations, you were retired in the year !!!
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Iteration (while statement)
The while statement has the following syntax:
while (selection)
code;
selection
true
false
code
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Iteration (while- sats)
import java.util.Scanner;
public class Counter {
public static void main (String [] args) {
Scanner scan = new Scanner (System.in);
int sum = 0;
int number;
int index = 1;
System.out.print ("Enter an integer:");
number = scan.nextInt ();
while (index <= number) {
sum += index; // sum = sum + index
index ++; // index = index + 1;
}
System.out.println ("1 + 2 + 3 + ..." + number + "=" + sum);
}
Enter an integer:9
1 + 2 + 3 + ...9=45
}
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Assign operators
Operator
Example
Equivalent
+=
-=
*=
/=
%=
x += y
x -= y
x *= y
x /= y
x %= y
x=x+y
x=x-y
x=x*y
x=x/y
x=x%y
Exempel:
int sum = 100;
int num = 50;
sum += num //Equivalent to: sum = sum + num
System.out.println (sum);//150
while (index <= number) {
sum += index; // sum = sum + index
index ++; // index = index + 1;
}
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Operators of increase and decrease
The expression:
i++;
is the same as:
i = i + 1;
Expression
Operation
The term's value
num++
++num
num---num
add 1
add 1
subtract 1
subtract 1
gamla värdet
nya värdet
gamla värdet
nya värdet
while (index <= number) {
sum += index; // sum = sum + index
index ++;
// index = index + 1;
}
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What is printed in the console window?
public class ÖkaMinska{
public static void main (String[] args){
int a = 5;
int b = 5;
int c = 10;
System.out.println(a++);
System.out.println(++b);
System.out.println(a);
System.out.println(b);
System.out.println(c++ + ++c);
}
}
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Iteration (for statement)
import java.util.Scanner;
public class Counter {
public static void main (String [] args) {
Scanner scan = new Scanner (System.in);
int sum = 0;
int number;
System.out.print ("Enter an integer:");
number = scan.nextInt ();
for (int index = 1; index <= number; index ++) {
sum = sum + index;
}
System.out.println ("1 + 2 + 3 + ..." + number + "=" + sum);
}
}
Skriv in ett heltal: 9
1+2+3+...9=45
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Iteration (for statement)
for (int
index =
1;
index <=
5;
index ++)
sats;
Initialization
2017-05-09
Condition
sida 24
counter
Magnus Wärja
Nested statements
public class TwentyOne {
public static void main (String [] args) {
Random random = new Random ();
Scanner scan = new Scanner (System.in);
int sum = 0;
int result;
boolean play = true;
while (play) {
sum += random.nextInt (6) + 1;
System.out.println ("Total:" + sum);
if (sum <=21) {
System.out.println ("Throw (Yes = 0 No = 1):");
result = scan.nextInt ();
if (result!= 0) {
play = false;
}
}
else {
play = false;
}
}
System.out.println ("Result:" + sum);
}
}
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Total:5
Throw (Yes = 0 No = 1): 0
Total:8
Throw (Yes = 0 No = 1): 0
Total:12
Throw (Yes = 0 No = 1): 0
Total:15
Throw (Yes = 0 No = 1): 1
Result:15
Magnus Wärja
Exercises
4.1 Iteration
What happens during execution:
public static void main (String[] args){
int x = 0;
while (x < 3){
x++;
System.out.println (x);
}}
4.2 Iteration
What happens during execution:
public static void main (String[] args){
for(int i = 1; i <= 3; i++){
System.out.println (i);
}}
4.3 Iteration
What happens during execution:
public static void main (String[] args){
int x = 10;
while (x != 3){
System.out.println (x);
x--;
}}
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Exercises
4.4 Iteration
What happens during execution:
public static void main (String[] args){
int x = 0;
while (x != 3 && x < 10){
x += 2;
System.out.println (x);
}
}
4.5 Iteration
What happens during execution:
public static void main (String[] args){
for(int i = 15; i >= 3; i -=3){
System.out.println (i);
}
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Exercises
4.6 Iteration
What happens during execution:
public static void main (String[] args){
Scanner scan = new Scanner(System.in);
double sum = 0; double average = 0;
int numbers = 0; int num;
System.out.print("Enter an integer: ");
num = scan.nextInt();
while (tal != 0){
System.out.print ("Enter a new integer: ");
num = scan.nextInt();
sum += tal;
numbers++;
}
if (numbers != 0)
average = sum / numbers;
System.out.println ("Average: " + average );
}
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Exercises
4.7 Iteration
What happens during execution:
public static void main (String[] args){
Scanner scan = new Scanner(System.in);
double sum = 0;
double average = 0;
int numbers = 0;
int num;
System.out.print("Enter an integer: : ");
num = scan.nextInt();
while (num != 0){
sum += tal;
numbers++;
System.out.print ("Enter a new integer: : ");
num = scan.nextInt();
}
if (numbers != 0)
average = sum / numbers;
System.out.println ("Average: " + average );
}
}
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Exercises
4.8 Mixed
Write a program that prints all the odd numbers from 1 to 99 (use a for loop).
4.9 Mixed
Write a program that computes the sum of all integers from 1 to 100 (use for loop).
4.10 Mixed
Write a program using a while loop that prints the text "ALARM!" repeatedly at separate lines. The user shall be able
to specify the number of times the "ALARM" to be written out.
4.11 Mixed
Write a program that reads five numbers and prints out the larger of the given numbers.
4.12 Mixed
Write a program that reads five numbers and prints the smallest and the largest of the given numbers.
4.13 Mixed
Write a program that reads a series of optional numbers and then prints the minimum and the maximum of the given numbers.
The process should be stopped by the number zero. If the first number is zero, the text shall be printed "No numbers
loaded"
4:14 Mixed
Write a program that reads a text string using the Scanner class. The program writes then the number of times the letter 'a’
appears in the loaded text string.
3:25 Mixed
Write a program that reads a name using the Scanner class. The program writes then every other character in the name
beginning with the first letter.
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Exercises
4.1 Iteration
What happens during execution
public static void main (String[] args){
int x = 0;
do{
x++;
System.out.println (x);
} while (x < 3);
}
4.2 Iteration
What happens during execution
public static void main (String[] args){
int x = 0;
while (x < 3){
x++;
System.out.println (x);
}}
4.3 Iteration
Ange resultatet vid exekvering
public static void main (String[] args){
for(int i = 1; i <= 3; i++){
System.out.println (i);
}}
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Array
An array is an ordered list of elements
The array name
Each element has an index
0
points
1
2
3
79 87 94 82
4
5
6
67 98 87
7
8
9
81 74
91
An array of size N is indexed from zero to N-1
This array holds 10 values that are indexed from 0 to 9
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Array
A particular value in an array can be accessed with the array name followed by the index in brackets
For example:
points [2]
gives the number 94 (the third number in our array)
The expression represents a place to store a single integer and can be used anywhere int variable is used
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Array
Ett element i en array kan tilldelas ett värde, skrivas ut, eller användas i en beräkning, osv
public class MyArray{
public static void main (String[] args){
int[] points = new int[10];
points [3] = 82;
points [2] = points[3] + 12;
System.out.println(points[2]);
System.out.println(points[2] / 2);
}
}
94
47
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Deklarera en array
Några deklarationer av arrayer:
int[] result= new int[10];
float[] price = new float[500];
boolean[] flag = new boolean[20];
char[] code = new char[1750];
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Arrayens gränser
myArray [100] have indices 0 to 99
Specifies one another index, you get:
ArrayIndexOutOfBoundsException ??
System.out.println (minArray [100]); // This produces an error?
It is common to accidentally counting too far in loops
problem
for (int index = 0; index <= 100; index ++)
minArray [index] = index * 50;
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Användning av Array
import java.util.Scanner;
public class Array{
public static void main(String[] args){
Scanner scan = new Scanner(System.in);
int num = 0;
int sum = 0;
int[] list = new int[5];
System.out.println("Enter five numbers: ");
for (int i = 0; i < 5; i ++){
System.out.print(”Enter a number: " + (i + 1) + ":");
num = scan.nextInt();
list[i] = num;
Enter five numbers::
}
Enter number 1:5
Enter number 2:6
for (int i = 0; i < 5; i ++){
Enter number 3:4
sum += list[i];
Enter number 4:8
}
Enter number 5:2
System.out.println("The total is: " + sum);
}
The total is: 25
}
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Exercises
5.1 Array
Write a Java program to sum values of an array.
5.2 Array
Write a Java program to calculate the average value of array elements.
5.3 Array
Write a Java program to test if an array contains a specific value.
5.4 Array
Write a Java program to find the index of an array element.
5.5 Array
Write a Java program to remove a specific element from an array.
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