Arrays 1

An array is a sequence of values
Used to store multiple values of the same type using a single variable
The size of the array is fixed, determined when created
The values in the array are called elements
Elements in arrays are accessed using an index
The index starts at 0, not 1

Creating Arrays

int[] data = new int[10];

double[] priceList;
priceList = new double[5];

String[] names = {"Ani", "Budi", "Cinta"};

Accessing Elements

Code
Ilustrasi

int[] counts = new int[4];

Code
Ilustrasi

counts[0] = 7;
counts[1] = counts[0] * 2;
counts[2]++;
counts[3] = counts[3] - 60;

Displaying Arrays

False
True
True

int[] values = {89, 50, 77};
System.out.println(values); // [I@15db9742

int[] values = {89, 50, 77};
System.out.println(values[0]);
System.out.println(values[1]);
System.out.println(values[2]);

int[] values = {89, 50, 77};
for (int i = 0; i < 3; i++) {
    System.out.println(values[i]);
}

Array length

.length : digunakan untuk mengetahui panjang array yang dimiliki oleh suatu array

int[] values = {89, 50, 77};
for (int i = 0; i < 3; i++) {
    System.out.println(values[i]);
}
for (int i = 0; i < values.length; i++) {
    System.out.println(values[i]);
}

Copying Arrays

False
True

int[] a = {89, 50, 77};
int[] b = a;
b[0] = b[0] - 20;
System.out.println(a[0]);
System.out.println(b[0]);

int[] a = {89, 50, 77};
int[] b = new int[a.length];
for (int i = 0; i < a.length; i++) {
    b[i] = a[i];   
}
int[] a = {89, 50, 77};
int[] b = Arrays.copyOf(a, a.length);
int[] c = Arrays.copyOf(a, 2);

Array Traversal

True
True

int[] values = {89, 50, 77};
for (int i = 0; i < values.length; i++) {
    System.out.println(values[i]);
}
for (int i = 0; i < values.length; i++) {
    values[i] = values[i] * 2;
}

int[] values = {89, 50, 77};
for (int v : values) {
    System.out.println(v);
}

String $\Leftrightarrow$ char Array

String word = "lemon";
char[] characters = word.toCharArray();

characters[0] = 'm';
characters[2] = 'l';

String word2 = String.valueOf(characters);

System.out.println(word2);

Exercise

Question 1
Answer 1

Create an array that can hold 15 integers
Fill up each element of the array with the number 123
Then display the contents of the array

int[] numbers = new int[15];
for (int i = 0; i < numbers.length; i++) {
    numbers[i] = 123;
}
for (int i = 0; i < numbers.length; i++) {
    System.out.println("Element-" + i + " = " + numbers[i]);
}

Question 2
Answer 2

Create an array that can hold 5 integers
Fill up the array with user inputs
Then display the contents of the array

Scanner scanner = new Scanner(System.in);
int[] numbers = new int[5];
for (int i = 0; i < numbers.length; i++) {
    System.out.print("Enter the value of Element-" + i + ": ");
    numbers[i] = scanner.nextInt();
}
for (int i = 0; i < numbers.length; i++) {
    System.out.println("Element-" + i + " = " + numbers[i]);
}

Question 3
Answer 3

Create an array that can hold $n$ integers
$n$ is user input
Fill up the array with user inputs
Then display the contents of the array

Scanner scanner = new Scanner(System.in);
System.out.print("Enter the Length of array: ");
int n = scanner.nextInt();
int[] numbers = new int[n];
for (int i = 0; i < numbers.length; i++) {
    System.out.print("Enter the value of Element-" + i + ": ");
    numbers[i] = scanner.nextInt();
}
for (int i = 0; i < numbers.length; i++) {
    System.out.println("Element-" + i + " = " + numbers[i]);
}

Question 4
Answer 4

Create an array that can hold $n$ integers
$n$ is user input
Fill up the array with user inputs
Then display the contents of the array starting from the last element to the first

Scanner scanner = new Scanner(System.in);
System.out.print("Enter the Length of array: ");
int n = scanner.nextInt();
int[] numbers = new int[n];
for (int i = 0; i < numbers.length; i++) {
    System.out.print("Enter the value of Element-" + i + ": ");
    numbers[i] = scanner.nextInt();
}
for (int i = numbers.length - 1; i >= 0; i--) {
    System.out.println("Element-" + i + " = " + numbers[i]);
}

Question 5
Answer 5

Create an array that can hold $n$ integers
$n$ is user input
Fill up the array with user inputs
Then display the contents of the array starting from the last element to the first

Scanner scanner = new Scanner(System.in);
System.out.print("How many values: ");
int n = scanner.nextInt();
int[] numbers = new int[n];
for (int i = 0; i < numbers.length; i++) {
    System.out.print("Enter the value-" + i + ": ");
    numbers[i] = scanner.nextInt();
}
double sum = 0;
for (int i = 0; i < numbers.length; i++) {
    sum += numbers[i];
}
double mean = sum / numbers.length;
double sumOfSquares = 0;
for (int i = 0; i < numbers.length; i++) {
    sumOfSquares += Math.pow(numbers[i] - mean, 2);
}
double standardDeviation = Math.sqrt(sumOfSquares / numbers.length);
System.out.println("Standard Deviation = " + standardDeviation);

Question 6
Answer 6

Make a program to check whether a word entered by a user is palindrome or not
A palindrome is a word, number, phrase, or other sequence of characters which reads the same backward as forward
Examples:
- eye
- level
- radar
- madam
- refer
- …

Scanner scanner = new Scanner(System.in);
System.out.print("Enter a word: ");
String word = scanner.next();
char[] characters = word.toCharArray();
boolean isPalindrome = true;
for (int i = 0; i < characters.length / 2; i++) {
    if (characters[i] != characters[characters.length - 1 - i]) {
        isPalindrome = false;
        break;
    }
}
if (isPalindrome) {
    System.out.println("Palindrome");
} else {
    System.out.println("Not a palindrome");
}

Question 7
Answer 7

Write a program that asks the user to enter the student’s name and grade n times.
After all data is entered, the user can search for the grade of a student by entering his name.
The program stops when the user enters “-” when asked for the name

Scanner scanner = new Scanner(System.in);
System.out.print("How many students? ");
int n = scanner.nextInt();
String[] names = new String[n];
int[] grades = new int[n];
for (int i = 0; i < n; i++) {
    System.out.print("Name of student-" + i + ": ");
    names[i] = scanner.next();
    System.out.print("Grade of student-" + i + ": ");
    grades[i] = scanner.nextInt();
}
while (true) {
    System.out.print("Searching the grade of: ");
    String name = scanner.next();
    if (name.equals("-")) {
        break;
    }
    boolean found = false;
    for (int i = 0; i < n; i++) {
        if (names[i].equals(name)) {
            System.out.println(name + "\'s grade is " + grades[i]);
            found = true;
            break;
        }
    }
    if (!found) {
        System.out.println("Student not found");
    }
}

Persiapan Belajar

Materi

Task

Programming by Doing

Compiler

Creating Arrays

Accessing Elements

Displaying Arrays

Array length

Copying Arrays

Array Traversal

String $\Leftrightarrow$ char Array

Exercise

​Creating Arrays

​Accessing Elements

​Displaying Arrays

​Array length

​Copying Arrays

​Array Traversal

​String ⇔\Leftrightarrow⇔ char Array

​Exercise

Creating Arrays

Accessing Elements

Displaying Arrays

Array length

Copying Arrays

Array Traversal

String $\Leftrightarrow$ char Array

Exercise