Java do-while Loop: Execute First, Then Judge to Avoid Unnecessary Loop Execution
The core of the do-while loop in Java is "execute the loop body first, then judge the condition", ensuring the loop body is executed at least once. It is suitable for scenarios where data needs to be processed at least once initially (such as user input validation). Its syntax structure is `do{ loop body }while(condition);`, and it should be noted that a semicolon must be added after while. Compared with the while loop (which judges first), it avoids the problem that the loop body does not execute when the initial condition is not met. For execution flow example: taking outputting 1-5 as an example, after initializing the variable, the loop body is executed, the variable is updated, and the condition is judged until the condition is not met to terminate. Common mistakes include: forgetting to update the loop variable causing an infinite loop, omitting the semicolon after while, or the condition failing to terminate the loop. This loop is applicable to scenarios where data must be processed first (such as reading files, user input interaction). To master its logic, attention should be paid to the correct update of the loop variable and the condition, ensuring the loop can terminate.
Read MoreJava while Loop: Repeating Execution While Conditions Are Met, with Examples
The Java `while` loop is used to repeatedly execute code, with the core idea being "execute the loop body as long as the condition is met, until the condition is no longer satisfied." The syntax is `while(conditionExpression) { loopBody }`, where the condition must be a boolean value, and the loop body is recommended to be enclosed in braces. Manually writing repeated code (e.g., printing numbers 1-5) is cumbersome when no loop is needed, whereas the `while` loop simplifies this. For example, to print 1-5: initialize `i=1`, then `while(i<=5)` executes the print statement and increments `i` (to avoid an infinite loop). When calculating the sum of numbers 1-10, initialize `sum=0` and `i=1`, then `while(i<=10)` adds `i` to `sum`, and the total sum (55) is printed. Infinite loops should be avoided: ensure the condition is never `true` permanently or that the condition variable is not modified (e.g., forgetting `i++`). Always include logic in the loop body that will make the condition `false`. The `do-while` loop is also introduced, which executes the loop body first and then checks the condition, guaranteeing execution at least once. In summary, the `while` loop is suitable for repeated scenarios where the condition is met (e.g., printing sequences, summing values). Be cautious of infinite loops, and proficiency will come with practice.
Read MoreJava For Loop: Simple Implementation for Repeated Operations, A Must-Learn for Beginners
This article introduces the relevant knowledge of for loops in Java. First, it points out that when code needs to be executed repeatedly in programming, loop structures can simplify operations and avoid tedious repetitions. The for loop is the most basic and commonly used loop, suitable for scenarios with a known number of iterations. Its syntax consists of three parts: initialization, condition judgment, and iteration update, which control the execution of the loop through these three parts. Taking printing numbers from 1 to 5 as an example, the article demonstrates the execution process of a for loop: initialize i=1, the condition is i<=5, and iterate with i++. The loop body prints the current number, and the loop ends when i=6, where the condition is no longer met. Classic applications are also listed, such as calculating the sum from 1 to 100 (sum via accumulation) and finding the factorial of 5 (factorial via multiplication). Finally, it emphasizes the key to avoiding infinite loops: ensuring correct condition judgment and iteration updates to prevent the loop variable from not being updated or the condition from always being true. Mastering the for loop enables efficient handling of repeated operations and lays the foundation for learning more complex loops in the future.
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