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Java Control Flow: If Statements and Loops

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1 + # Java Control Flow: If Statements and Loops
2 +
3 + ## If Statements
4 +
5 + ### Basic If Statement
6 + The simplest form of decision making:
7 +
8 + ```java
9 + public class BasicIf {
10 + public static void main(String[] args) {
11 + int temperature = 28;
12 +
13 + if (temperature > 25) {
14 + System.out.println("It's a hot day!");
15 + }
16 +
17 + // Using multiple conditions
18 + if (temperature > 25 && temperature < 30) {
19 + System.out.println("Perfect weather for swimming!");
20 + }
21 + }
22 + }
23 + ```
24 +
25 + ### If-Else Statement
26 + When you need to handle two alternative scenarios:
27 +
28 + ```java
29 + public class IfElse {
30 + public static void main(String[] args) {
31 + int score = 75;
32 +
33 + if (score >= 60) {
34 + System.out.println("You passed!");
35 + } else {
36 + System.out.println("You need to retake the test.");
37 + }
38 +
39 + // Using with String comparison
40 + String status = "Premium";
41 + if (status.equals("Premium")) {
42 + System.out.println("Access granted to premium features");
43 + } else {
44 + System.out.println("Upgrade to premium for additional features");
45 + }
46 + }
47 + }
48 + ```
49 +
50 + ### If-Else-If Ladder
51 + For multiple conditions:
52 +
53 + ```java
54 + public class IfElseIf {
55 + public static void main(String[] args) {
56 + int grade = 85;
57 +
58 + if (grade >= 90) {
59 + System.out.println("A - Excellent!");
60 + } else if (grade >= 80) {
61 + System.out.println("B - Good job!");
62 + } else if (grade >= 70) {
63 + System.out.println("C - Satisfactory");
64 + } else if (grade >= 60) {
65 + System.out.println("D - Needs improvement");
66 + } else {
67 + System.out.println("F - Failed");
68 + }
69 + }
70 + }
71 + ```
72 +
73 + ### Nested If Statements
74 + Conditions within conditions:
75 +
76 + ```java
77 + public class NestedIf {
78 + public static void main(String[] args) {
79 + boolean isLoggedIn = true;
80 + String userRole = "admin";
81 +
82 + if (isLoggedIn) {
83 + System.out.println("Welcome back!");
84 +
85 + if (userRole.equals("admin")) {
86 + System.out.println("You have admin privileges");
87 + } else {
88 + System.out.println("You have user privileges");
89 + }
90 + } else {
91 + System.out.println("Please log in first");
92 + }
93 + }
94 + }
95 + ```
96 +
97 + ## Loops
98 +
99 + ### For Loop
100 + Used when you know the number of iterations:
101 +
102 + ```java
103 + public class ForLoop {
104 + public static void main(String[] args) {
105 + // Basic for loop
106 + for (int i = 0; i < 5; i++) {
107 + System.out.println("Count: " + i);
108 + }
109 +
110 + // Loop with multiple variables
111 + for (int i = 0, j = 10; i < j; i++, j--) {
112 + System.out.println("i = " + i + ", j = " + j);
113 + }
114 +
115 + // For loop with array
116 + int[] numbers = {1, 2, 3, 4, 5};
117 + for (int i = 0; i < numbers.length; i++) {
118 + System.out.println("Number: " + numbers[i]);
119 + }
120 + }
121 + }
122 + ```
123 +
124 + ### Enhanced For Loop (For-Each)
125 + Simplified loop for collections and arrays:
126 +
127 + ```java
128 + public class EnhancedFor {
129 + public static void main(String[] args) {
130 + String[] fruits = {"Apple", "Banana", "Orange", "Mango"};
131 +
132 + for (String fruit : fruits) {
133 + System.out.println("Fruit: " + fruit);
134 + }
135 +
136 + // With ArrayList
137 + ArrayList<Integer> numbers = new ArrayList<>();
138 + numbers.add(1);
139 + numbers.add(2);
140 + numbers.add(3);
141 +
142 + for (Integer number : numbers) {
143 + System.out.println("Number: " + number);
144 + }
145 + }
146 + }
147 + ```
148 +
149 + ### While Loop
150 + Used when the number of iterations is not known in advance:
151 +
152 + ```java
153 + public class WhileLoop {
154 + public static void main(String[] args) {
155 + int count = 0;
156 +
157 + while (count < 5) {
158 + System.out.println("Count: " + count);
159 + count++;
160 + }
161 +
162 + // Reading input example
163 + Scanner scanner = new Scanner(System.in);
164 + String input = "";
165 +
166 + while (!input.equals("quit")) {
167 + System.out.println("Enter command (type 'quit' to exit):");
168 + input = scanner.nextLine();
169 + System.out.println("You entered: " + input);
170 + }
171 + }
172 + }
173 + ```
174 +
175 + ### Do-While Loop
176 + Ensures the loop body executes at least once:
177 +
178 + ```java
179 + public class DoWhile {
180 + public static void main(String[] args) {
181 + int number = 1;
182 +
183 + do {
184 + System.out.println("Number: " + number);
185 + number *= 2;
186 + } while (number < 100);
187 +
188 + // Menu example
189 + Scanner scanner = new Scanner(System.in);
190 + int choice;
191 +
192 + do {
193 + System.out.println("\n1. View profile");
194 + System.out.println("2. Edit settings");
195 + System.out.println("3. Exit");
196 + System.out.print("Enter your choice: ");
197 +
198 + choice = scanner.nextInt();
199 +
200 + switch (choice) {
201 + case 1:
202 + System.out.println("Viewing profile...");
203 + break;
204 + case 2:
205 + System.out.println("Editing settings...");
206 + break;
207 + case 3:
208 + System.out.println("Goodbye!");
209 + break;
210 + default:
211 + System.out.println("Invalid choice!");
212 + }
213 + } while (choice != 3);
214 + }
215 + }
216 + ```
217 +
218 + ### Control Statements in Loops
219 + Break and continue statements:
220 +
221 + ```java
222 + public class LoopControl {
223 + public static void main(String[] args) {
224 + // Break example
225 + for (int i = 0; i < 10; i++) {
226 + if (i == 5) {
227 + break; // Exit loop when i equals 5
228 + }
229 + System.out.println("Count: " + i);
230 + }
231 +
232 + // Continue example
233 + for (int i = 0; i < 5; i++) {
234 + if (i == 2) {
235 + continue; // Skip iteration when i equals 2
236 + }
237 + System.out.println("Number: " + i);
238 + }
239 + }
240 + }
241 + ```
242 +
243 + Key points to remember:
244 + - If statements can be nested but try to avoid too many levels of nesting
245 + - Always use curly braces for clarity, even for single-line blocks
246 + - Choose the appropriate loop based on your needs:
247 + - For loop when you know the number of iterations
248 + - While loop when the iteration count is unknown
249 + - Do-while when you need at least one iteration
250 + - Use break to exit a loop early
251 + - Use continue to skip to the next iteration
252 + - Be careful with infinite loops - ensure your loop condition will eventually be false
253 +
254 + These control flow statements are fundamental to Java programming and are used extensively in real-world applications.
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