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Java Programming for Beginners: Chapter 3 - Control Flow in Java |
Understanding Control Flow in Java
In this chapter, we'll delve deeper into control flow structures in Java and learn how to use them effectively in our programs. Control flow structures allow us to control the flow of execution based on certain conditions, enabling us to create more dynamic and interactive applications.
1. if-else Statements
The if-else statement is one of the most fundamental control flow structures in Java. It allows us to execute a block of code if a specified condition is true, and an alternative block of code if the condition is false.
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int x = 10; if (x > 0) { System.out.println("x is positive"); } else { System.out.println("x is non-positive"); }
In this example, if the value of x is greater than 0, the message "x is positive" will be printed. Otherwise, the message "x is non-positive" will be printed.
2. Nested if-else Statements
Nested if-else statements allow us to create more complex conditions by nesting one if-else statement inside another.
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int num = 10; if (num > 0) { if (num % 2 == 0) { System.out.println("num is positive and even"); } else { System.out.println("num is positive and odd"); } } else { System.out.println("num is non-positive"); }
In this example, we first check if num is positive. If it is, we then check if it's even or odd. If num is not positive, we print "num is non-positive".
3. switch Statements
The switch statement provides a convenient way to handle multiple possible values of a variable or expression.
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int dayOfWeek = 3; String dayName; switch (dayOfWeek) { case 1: dayName = "Monday"; break; case 2: dayName = "Tuesday"; break; case 3: dayName = "Wednesday"; break; case 4: dayName = "Thursday"; break; case 5: dayName = "Friday"; break; case 6: dayName = "Saturday"; break; case 7: dayName = "Sunday"; break; default: dayName = "Invalid day"; break; } System.out.println("Today is " + dayName);
In this example, we use a switch statement to determine the day of the week based on the value of dayOfWeek. The break statement is used to exit the switch block after a match is found.
4. Loops
Loops are used to repeat a block of code multiple times until a certain condition is met. Java supports three types of loops: for, while, and do-while.
a. for Loop
The for loop is used to iterate over a sequence of values for a predetermined number of times.
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for (int i = 1; i <= 5; i++) { System.out.println("Count: " + i); }
In this example, the loop will iterate five times, printing the value of i on each iteration.
b. while Loop
The while loop is used to repeat a block of code as long as a specified condition is true.
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int i = 1; while (i <= 5) { System.out.println("Count: " + i); i++; }
In this example, the loop will continue iterating as long as the value of i is less than or equal to 5.
c. do-while Loop
The do-while loop is similar to the while loop, but it always executes the block of code at least once, even if the condition is false.
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int i = 1; do { System.out.println("Count: " + i); i++; } while (i <= 5);
In this example, the loop will execute once, even though the condition i <= 5 is initially false.
5. Break and Continue Statements
The break statement is used to exit a loop prematurely, while the continue statement is used to skip the rest of the code inside a loop and continue with the next iteration
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for (int i = 1; i <= 10; i++) { if (i == 5) { break; // Exit the loop when i equals 5 } if (i % 2 == 0) { continue; // Skip even numbers } System.out.println("Number: " + i); }
In this example, the loop will print odd numbers from 1 to 10, excluding the number 5.
Conclusion
Understanding control flow structures is essential for writing effective Java programs. By mastering if-else statements, switch statements, loops, and related concepts, you'll be able to create more sophisticated and dynamic applications. Practice using these control flow structures in your code to become more comfortable with their syntax and behavior.