ArrayList Lesson
Practicing ArrayLists
interface Turtle {
}
// create ArrayLists that satisfy the following
// a) that stores Boolean values
ArrayList<Boolean> booleans = new ArrayList<Boolean>();
// b) that stores Turtle Objects
ArrayList<Turtle> turtles = new ArrayList<Turtle>();
// c) that initializes with 10 Strings
ArrayList<String> strings = new ArrayList<String>(10);
import java.util.ArrayList;
public class Hack2 {
public static void main(Integer[] args) {
ArrayList<Integer> randomNumbers = new ArrayList<Integer>();
randomNumbers.add(1);
randomNumbers.add(4);
randomNumbers.add(7);
randomNumbers.add(12);
randomNumbers.add(23);
System.out.println("ArrayList: " + randomNumbers);
randomNumbers.remove(3);
randomNumbers.sort(Comparator.naturalOrder());
randomNumbers.add(14);
System.out.println(randomNumbers);
}
}
Hack2.main(null);
public class Hack3 {
public static void main(String[] args) {
ArrayList<Integer> values = new ArrayList<Integer>();
values.add(1);
values.add(4);
values.add(7);
values.add(12);
values.add(23);
System.out.println("ArrayList: " + values);
int total = 0;
for (int i=0; i < values.size(); i++) {
total += values.get(i);
}
System.out.println(total);
}
}
Hack3.main(null);
int[] arr = {1, 3, 5, 23, 5, 12, 5, 7, 12, 4};
for (int i = 0; i < arr.length; i++) {
// nested loop 1 index ahead
for (int j = i + 1; j < arr.length; j++) {
// comparing elements
int temp = 0;
if (arr[j] < arr[i]) {
// write the swap code!
temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
}
// Printing sorted array
System.out.print(arr[i] + " ");
}
// code here
int[] arr = {12, 4, 12, 3, 45, 5, 2, 4};
// Even
for (int i = 0; i < arr.length; i += 2) {
System.out.println(arr[i]);
}
// Odd
for (int i = 1; i < arr.length; i += 2) {
System.out.println(arr[i]);
}
// code here
int[][] arr2 = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
for (int[] row : arr2) {
for (int num : row) {
System.out.print(num + " ");
}
System.out.println();
}
public class Test1
{
public static void main(String[] args)
{
int[][] array = { {1,2,3},{-1,-2,-3},{4,5,6} };
int total = 0;
//ADD CODE HERE
for (int i = 0; i < array.length; i++) {
for (int j = 0; j < array[i].length; j++) {
if (i == j) {
total += array[i][j];
}
}
}
System.out.println(total);
}
}
Test1.main(null);
// code here
public static boolean double23(int[] nums) {
int twoCount = 0;
int threeCount = 0;
for (int num : nums) {
if (num == 2) {
twoCount++;
} else if (num == 3) {
threeCount++;
}
}
if (twoCount == 2 || threeCount == 2) {
return true;
}
return false;
}
System.out.println(double23(new int[]{2, 2, 3}));
// code here
public class findNumber {
public static int find(int[][] arr, int n) {
int count = 0;
for (int[] row : arr) {
for (int num : row) {
if (num == n) {
count++;
}
}
}
return count;
}
}
findNumber.find(new int[][]{{1, 2, 3}}, 2);
public class SeatingChart {
private ArrayList<String> chart;
SeatingChart(ArrayList<String> chart) {
this.chart = chart;
}
public void alphabetize() {
String temp1 = "";
String temp2 = "";
for (int i = 0; i < chart.size() - 1; i++) {
for (int j = i + 1; j < chart.size(); j++) {
if (chart.get(i).compareTo(chart.get(j)) > 0) {
temp2 = chart.remove(j);
chart.add(i, temp2);
temp1 = chart.remove(i + 1);
chart.add(j, temp1);
}
}
}
}
public void add(String person) {
chart.add(person);
}
public void delete(int index) {
chart.remove(index);
}
public String toString() {
String response = "";
for (String person : chart) {
response += person + " ";
}
return response;
}
}
class Tester {
public static void main(String[] args) {
SeatingChart chart = new SeatingChart(new ArrayList<String>(List.of("Don", "Bailey", "Evan")));
System.out.println(chart);
chart.alphabetize();
System.out.println(chart);
chart.add("Hetvi");
chart.add("Iris");
chart.add("Ellen");
chart.add("Nod");
chart.alphabetize();
System.out.println(chart);
chart.delete(6);
System.out.println(chart);
}
}
Tester.main(null);
public class Phrase {
private String currentPhrase;
/** Constructs a new Phrase object. */
public Phrase (String p) {
currentPhrase = p;
}
/** Returns the index of the nth occurrence of str in the current phrase;
* returns -1 if the nth occurrence does not exist.
* Precondition: str.length () > 0 and n > 0
* Postcondition: the current phrase is not modified.
*/
public int findNthOccurrence(String str, int n) {
int counter = 0;
for (int i = 0; i < currentPhrase.length() - str.length() + 1; i++) {
if (currentPhrase.substring(i, i + str.length()).equals(str)) {
counter++;
if (counter == n) {
return i;
}
}
}
return -1;
}
/* implementation not shown */
/** Modifies the current phrase by replacing the nth occurrence of str with repl.
* If the nth occurrence does not exist, the current phrase is unchanged.
* Precondition: str.length () > 0 and n > 0
*/
public void replaceNthOccurrence(String str, int n, String repl) {
/* to be implemented in part (a) */
int index = findNthOccurrence(str, n);
if (index != -1) {
currentPhrase = currentPhrase.substring(0, index) + repl + currentPhrase.substring(index + str.length(), currentPhrase.length());
}
}
/** Returns the index of the last occurrence of str in the current phrase;
* returns -1 if str is not found.
* Precondition: str.length () > 0
* Postcondition: the current phrase is not modified.
*/
public int findLastOccurrence(String str) {
/* to be implemented in part (b) */
int index = -1;
for (int i = 0; i < currentPhrase.length() - str.length(); i++) {
if (currentPhrase.substring(i, i + str.length()).equals(str)) {
index = i;
}
}
return index;
}
/** Returns a string containing the current phrase. */
public String toString() {
return currentPhrase;
}
}
class Tester {
public static void main(String[] args) {
Phrase p1 = new Phrase("I love to code code code");
System.out.println(p1.findNthOccurrence("code", 1));
p1.replaceNthOccurrence("code", 3, "in CSA!");
System.out.println(p1);
System.out.println(p1.findLastOccurrence("code"));
}
}
Tester.main(null);