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2 files changed, 29 insertions

ArrayListExamples.java

@@ -117,6 +117,7 @@ public class ArrayListExamples {
117 117 System.out.printf("\nNew Cart Total: $%.2f\n", total);
118 118
119 119 // Sort by price (using Comparator)
120 + // Look BELOW for some explanation of this...
120 121 Collections.sort(cart, new Comparator<CartItem>() {
121 122 @Override
122 123 public int compare(CartItem item1, CartItem item2) {

explain.md(fichier créé)

@@ -0,0 +1,28 @@
1 + ## Explaining the Sort thing in the Cart
2 +
3 +
4 + This code is sorting a list of shopping cart items by price using Java's Collections.sort method. Let me break it down:
5 +
6 + ```java
7 + Collections.sort(cart, new Comparator<CartItem>() {
8 + @Override
9 + public int compare(CartItem item1, CartItem item2) {
10 + return Double.compare(item1.getPrice(), item2.getPrice());
11 + }
12 + });
13 + ```
14 +
15 + Here's what each part does:
16 +
17 + 1. `Collections.sort(cart, ...)` - This is calling Java's built-in sort method on a collection named "cart" which contains CartItem objects.
18 +
19 + 2. `new Comparator<CartItem>() { ... }` - This creates an anonymous inner class that implements the Comparator interface specifically for CartItem objects. The Comparator defines how two CartItems should be compared.
20 +
21 + 3. `@Override public int compare(CartItem item1, CartItem item2)` - This overrides the compare method from the Comparator interface. It takes two CartItem objects and returns an integer that indicates their relative ordering.
22 +
23 + 4. `return Double.compare(item1.getPrice(), item2.getPrice());` - This compares the prices of the two cart items using Double.compare (which handles special cases like NaN values properly). It will return:
24 + - A negative value if item1's price is less than item2's price
25 + - Zero if the prices are equal
26 + - A positive value if item1's price is greater than item2's price
27 +
28 + After this code executes, the "cart" collection will be sorted in ascending order by price, with the cheapest items first and the most expensive items last.

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1 file changed, 2 insertions

ArrayListExamples.java

@@ -3,6 +3,8 @@ import java.util.Collections;
3 3 import java.util.Comparator;
4 4 import java.util.Scanner;
5 5
6 +
7 + // See below for information on this class.
6 8 public class ArrayListExamples {
7 9
8 10 public static void main(String[] args) {

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1 file changed, 0 insertions, 0 deletions

usingarraylistj.md renommé en usingarraylists.md

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kristofer's Avatar kristofer a révisé ce gist 1740492082. Aller à la révision

2 files changed, 207 insertions

ArrayListExamples.java(fichier créé)

@@ -0,0 +1,184 @@
1 + import java.util.ArrayList;
2 + import java.util.Collections;
3 + import java.util.Comparator;
4 + import java.util.Scanner;
5 +
6 + public class ArrayListExamples {
7 +
8 + public static void main(String[] args) {
9 + // Example 1: Student Management System
10 + studentManagementSystem();
11 +
12 + System.out.println("\n-----------------------------------\n");
13 +
14 + // Example 2: Shopping Cart Implementation
15 + shoppingCartExample();
16 + }
17 +
18 + /**
19 + * Example 1: Student Management System
20 + * Demonstrates adding, removing, searching, and sorting students
21 + */
22 + public static void studentManagementSystem() {
23 + System.out.println("STUDENT MANAGEMENT SYSTEM EXAMPLE");
24 +
25 + // Create an ArrayList to store student names
26 + ArrayList<String> students = new ArrayList<>();
27 +
28 + // Add students to the list
29 + students.add("Emma Johnson");
30 + students.add("Liam Smith");
31 + students.add("Olivia Williams");
32 + students.add("Noah Brown");
33 + students.add("Ava Jones");
34 +
35 + // Display all students
36 + System.out.println("Current Students:");
37 + for (int i = 0; i < students.size(); i++) {
38 + System.out.println((i + 1) + ". " + students.get(i));
39 + }
40 +
41 + // Add a new student at a specific position (third position)
42 + students.add(2, "Mason Davis");
43 + System.out.println("\nAfter adding Mason Davis at position 3:");
44 + displayList(students);
45 +
46 + // Check if a student exists
47 + String searchName = "Ava Jones";
48 + if (students.contains(searchName)) {
49 + System.out.println("\nFound student: " + searchName);
50 + System.out.println("Position: " + (students.indexOf(searchName) + 1));
51 + } else {
52 + System.out.println("\nStudent not found: " + searchName);
53 + }
54 +
55 + // Remove a student
56 + students.remove("Noah Brown");
57 + System.out.println("\nAfter removing Noah Brown:");
58 + displayList(students);
59 +
60 + // Sort students alphabetically
61 + Collections.sort(students);
62 + System.out.println("\nAlphabetically sorted students:");
63 + displayList(students);
64 +
65 + // Clear the entire list
66 + students.clear();
67 + System.out.println("\nAfter clearing the list, size: " + students.size());
68 + }
69 +
70 + /**
71 + * Example 2: Shopping Cart Implementation
72 + * Demonstrates a more complex ArrayList with custom objects
73 + */
74 + public static void shoppingCartExample() {
75 + System.out.println("SHOPPING CART EXAMPLE");
76 +
77 + // Create an ArrayList of items
78 + ArrayList<CartItem> cart = new ArrayList<>();
79 +
80 + // Add items to cart
81 + cart.add(new CartItem("Laptop", 899.99, 1));
82 + cart.add(new CartItem("Mouse", 24.99, 1));
83 + cart.add(new CartItem("Keyboard", 59.99, 1));
84 + cart.add(new CartItem("USB Drive", 19.99, 2));
85 +
86 + // Display cart contents
87 + System.out.println("Shopping Cart Contents:");
88 + displayCart(cart);
89 +
90 + // Calculate and display total
91 + double total = 0;
92 + for (CartItem item : cart) {
93 + total += item.getPrice() * item.getQuantity();
94 + }
95 + System.out.printf("\nCart Total: $%.2f\n", total);
96 +
97 + // Update quantity of an item
98 + for (CartItem item : cart) {
99 + if (item.getName().equals("USB Drive")) {
100 + item.setQuantity(3);
101 + System.out.println("\nUpdated USB Drive quantity to 3");
102 + break;
103 + }
104 + }
105 +
106 + // Display updated cart and total
107 + System.out.println("\nUpdated Shopping Cart:");
108 + displayCart(cart);
109 +
110 + // Recalculate total
111 + total = 0;
112 + for (CartItem item : cart) {
113 + total += item.getPrice() * item.getQuantity();
114 + }
115 + System.out.printf("\nNew Cart Total: $%.2f\n", total);
116 +
117 + // Sort by price (using Comparator)
118 + Collections.sort(cart, new Comparator<CartItem>() {
119 + @Override
120 + public int compare(CartItem item1, CartItem item2) {
121 + return Double.compare(item1.getPrice(), item2.getPrice());
122 + }
123 + });
124 +
125 + System.out.println("\nCart Items Sorted by Price (Low to High):");
126 + displayCart(cart);
127 +
128 + // Remove an item
129 + cart.removeIf(item -> item.getName().equals("Mouse"));
130 + System.out.println("\nAfter removing Mouse:");
131 + displayCart(cart);
132 + }
133 +
134 + // Helper method to display a list of strings
135 + private static void displayList(ArrayList<String> list) {
136 + for (int i = 0; i < list.size(); i++) {
137 + System.out.println((i + 1) + ". " + list.get(i));
138 + }
139 + }
140 +
141 + // Helper method to display cart items
142 + private static void displayCart(ArrayList<CartItem> cart) {
143 + for (int i = 0; i < cart.size(); i++) {
144 + CartItem item = cart.get(i);
145 + System.out.printf("%d. %-10s $%.2f x %d = $%.2f\n",
146 + i + 1,
147 + item.getName(),
148 + item.getPrice(),
149 + item.getQuantity(),
150 + item.getPrice() * item.getQuantity());
151 + }
152 + }
153 + }
154 +
155 + /**
156 + * Class representing an item in a shopping cart
157 + */
158 + class CartItem {
159 + private String name;
160 + private double price;
161 + private int quantity;
162 +
163 + public CartItem(String name, double price, int quantity) {
164 + this.name = name;
165 + this.price = price;
166 + this.quantity = quantity;
167 + }
168 +
169 + public String getName() {
170 + return name;
171 + }
172 +
173 + public double getPrice() {
174 + return price;
175 + }
176 +
177 + public int getQuantity() {
178 + return quantity;
179 + }
180 +
181 + public void setQuantity(int quantity) {
182 + this.quantity = quantity;
183 + }
184 + }

usingarraylistj.md(fichier créé)

@@ -0,0 +1,23 @@
1 + I'll share some practical examples of using the ArrayList class in Java, focusing on different real-world scenarios.
2 +
3 + These examples demonstrate two common use cases for ArrayLists in Java:
4 +
5 + ### Example 1: Student Management System
6 + The first example shows how to use an ArrayList to manage a list of students, demonstrating:
7 + - Adding students to the list
8 + - Inserting a student at a specific position
9 + - Searching for students
10 + - Removing students
11 + - Sorting the list alphabetically
12 + - Clearing the entire list
13 +
14 + ### Example 2: Shopping Cart Implementation
15 + The second example is more complex, using an ArrayList to manage a shopping cart with custom objects:
16 + - Creating and storing custom objects (CartItem class)
17 + - Calculating totals from the items in the list
18 + - Finding and updating specific items in the list
19 + - Sorting items by price using a Comparator
20 + - Removing items conditionally with the removeIf() method
21 +
22 + These examples showcase the flexibility of ArrayList and how it can be used to manage both simple collections of strings and more complex collections of custom objects. Each example includes helpful methods for displaying the current state of the list, making it easier to understand how ArrayLists work in practice.
23 +
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