Arrays. Loops

AGENDA
Arrays
While
For
Break, continue
Search item in the array
Sorting
Practical tasks

An array is a container object that holds a fixed number of values of a single type. The length of an array is established when the array is created. After creation, its length is fixed.
String dayWeek[]= new String[7];
String[] month;
month = new String[12];
Each item in an array is called an element, and each element is accessed by its numerical index. As shown in the preceding illustration, numbering begins with 0.
dayWeek[0] = ″Monday″;
month[11] = ″December″;
Array

int[] monthDays = {31, 28, 31, 30, 31, 30,
31, 31, 30, 31, 30, 31} ;
int[] monthDays = new int[12];
monthDays[0] = 31;
monthDays[1] = 28;
// . . .
monthDays[11] = 31;
int n = monthDays.length; // n = 12
System.out.println(monthDays); //[I@659e0bfd
Need override toString();
or use Arrays.toString(monthDays);
Array

char twod1[][]= new char[3][4];
char[][] twod2= new char[3][4];
double[][] m= { {0, 1, 2, 3},
{4, 5, 6, 7},
{8, 9, 10, 11},
{12, 13, 14, 15} };
int[][] twoD= new int[4][];
twoD[0]= new int[5];
twoD[1]= new int[2];
twoD[2]= new int[3];
twoD[3]= new int[7];
int[][] irregular={{1},{2,3,4},{5},{6,7}}; // Rows not equal
Array
double m[4][4]; // Error;

while
A while loop statement repeatedly executes a target statement as long as a given condition is true.
while (condition){
statements;
}
What will be displayed?
int number = 0;
while (number <= 5) {
System.out.println(number);
number++;
}

do while
The difference between do-while and while is that do-while evaluates its expression at the bottom of the loop instead of the top. Therefore, the statements within the do block are always executed at least once
do {
statements;
} while (condition);
What will be displayed?
int i = 0;
do {
System.out.print(++i);
} while (i < 5);

The for statement provides a compact way to iterate over a range of values.
for
What will be displayed?
int[] numbers = {5, 6, 8, 3, 5, 7, 9};
for(int i = 0; i < numbers.length; i++){
System.out.println(numbers[i]);
}
for (init; condition; increment) {
statement(s);
}

Another representation of statement for
for
for (type variable : collection) {
statement(s);
}
int[] workHours = { 8, 6, 8, 7, 7 };
for (int h = 0; h < workHours.length; h++) {
System.out.println(workHours[h]);
}
or
for (int h : workHours) {
System.out.println(h);
}

The break statement terminates the for, while and do-while loop
break
What will be displayed?
Scanner sc = new Scanner(System.in);
int n = 0;
for (int i = 0; i < 5; i++) {
System.out.println("Input number");
n = Integer.parseInt(sc.nextLine());
if (n < 0){
break;
}
}
System.out.println(n);
sc.close();

The continue statement skips the current iteration the for, while and do-while loop
continue
What will be displayed?
Scanner sc = new Scanner(System.in);
int sum = 0;
int n;
for (int i = 0; i < 5; i++) {
System.out.println("Input number");
n = Integer.parseInt(sc.nextLine());
if (n < 0){
continue;
}
sum += n;
}
System.out.println(sum);
sc.close();

There’s an array int[] arr = {2, -5, 7, -4, 8};
What will results after running next code?
Sum, product, amount
int product = 1;
for (int i = 0; i < 5; i++) {
if (arr[i] > 0) {product = product * arr[i];}}
System.out.println("Product = " + product);
int amount = 0;
for (int a : arr) {
if (a > 0 && a <= 7) { amount++; }
}
System.out.println("Amount = " + amount);
int sum = 0;
for (int i = 0; i < arr.length; i++) { sum += arr[i];}
System.out.println("Sum = " + sum);

Minimum, maximum ...
There’s an array int[] arr = {2, -5, 7, -4, 8};
What will be results after running next code?
int max = arr[0];
int imax = 0;
int i = 0;
while (i < arr.length) {
if (arr[i] > max) {
max = arr[i];
imax = i;
}
i++;
}
System.out.print("Maximum = " + max);
System.out.println(" is in " + (imax + 1) + " place");

Sorting
There’s an array int[] arr = {2, -5, 7, -4, 8};
What will be results after running next code?
int tmp;
for (int i = 0; i < arr.length - 1; i++) {
for (int j = i + 1; j < arr.length; j++) {
if (arr[i] < arr[j]) {
tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
}
}
for (int i = 0; i < arr.length; i++) {
System.out.println(arr[i]);
}
Sorting elements by descending
using Bubble Sort

The Arrays class
The Arrays class in java.util package is a part of the Java Collection Framework.
This class provides methods to dynamically create and access arrays.
void sort(originalArray) sorts the complete array in ascending order.
int binarySearch(elementToBeSearched) searches for the specified element in the array with the help of Binary Search algorithm.
String toString(originalArray) returns a String representation of the contents of this Arrays.

The Arrays class
Example:
int[] numbers = { 2, -5, 8, -4, 7 };
Arrays.sort(numbers);
int index = Arrays.binarySearch(numbers, 7);
String elements = Arrays.toString(numbers);
System.out.println("Numbers = " + elements);
System.out.println(“Position of element with value 7 is " + index);
Numbers = [-5, -4, 2, 7, 8]
Element with value 7 was found in 3-th position

JUnit is a unit testing framework for the Java programming language.
JUnit has been important in the development of test-driven development, and is one of a family of unit testing frameworks collectively known as xUnit that originated with SUnit.
Testing Problems
Programmers should write tests
As you probably know programmers always busy, and they have no time to write tests
They need some tool that can help them
Main requirements for this tool:
A few lines of code then test should run
To write test that won’t run, then write the code that will make run
JUnit Framework

Mr. Erich Gamma who is a one of developers of JUnit framework also known as a Eclipse IDE developer
JUnit well integrated into Eclipse IDE
JUnit plugin for Eclipse IDE

JUnit assertion methods

JUnit

JUnit

public class Calc {
public int add(int a, int b) {
return a + b;
}
public int div(int a, int b){
return a / b;
}
}
Class Calc

import static org.junit.Assert.*;
import org.junit.Test;
public class CalcTest {
Calc calc = new Calc(); @Test
public void testAdd() { assertTrue(calc.add(1, 5) == 6);}
@Test
public void testDivPositive() {
int actual = 4;
int expected = calc.div(9, 2);
assertEquals(actual, expected);
}
@Test(expected = Exception.class)
public void testDivZero() {
int actual = calc.div(23, 0);
}
}
Class CalcTest

Create an array of ten integers. Display
the biggest of these numbers;
the sum of positive numbers in the array;
the amount of negative numbers in the array.
What values there are more: negative or positive?
Create a class Employee with fields name, department number, salary. Create five objects of class Employee. Display
all employees of a certain department (enter department number in the console);
arrange workers by the field salary in descending order.
Practical tasks

UDEMY course "Java Tutorial for Complete Beginners": https://www.udemy.com/java-tutorial/
Complete lessons 8, 9, 12, 14 - 16:
HomeWork (online course)

Ask user to enter the number of month. Read the value and write the amount of days in this month (create array with amount days of each month).
Enter 10 integer numbers. Calculate the sum of first 5 elements if they are positive or product of last 5 element in the other case.
Enter 5 integer numbers. Find
position of second positive number;
minimum and its position in the array.
Organize entering integers until the first negative number. Count the product of all entered even numbers.
Create class Car with fields type, year of production and engine capacity. Create and initialize four instances of class Car. Display cars
certain model year (enter year in the console);
ordered by the field year.
5*. Add Unit Tests to each task, publish code on GitHub
Homework

Short step-by-step online course:
https://www.udemy.com/junit-tutorial-for-beginners-with-java-examples/learn/v4/overview
Unit Testing with JUnit