Question

What does the following program segment do? for ( i = 1; i <= 5; i++ ) { for ( j = 1; j <= 3; j++ ) { for ( k = 1; k <= 4; k++ ) System.out.print( '*' ); System.out.println(); } // end inner for System.out.println(); } // end outer for

Short answer

The program prints 5 blocks of 3 lines; each line has 4 asterisks, with a blank line between blocks.

Step-by-step solution

Understanding the Outer Loop

The outer loop is a for loop that runs the variable \( i \) from 1 to 5. This loop will run 5 times in total. Each iteration represents one complete cycle of the inner set of operations, which includes two nested loops.

Exploring the Middle Loop

The middle loop is a for loop that runs the variable \( j \) from 1 to 3. For each iteration of the outer loop (\( i \)), the middle loop will execute 3 times. This means that the operations inside the third nested loop and the printing operation following it will be executed 3 times for each \( i \).

Observing the Innermost Loop

The innermost loop is a for loop that runs the variable \( k \) from 1 to 4. For each combination of \( i \) and \( j \), it executes 4 times, printing the asterisk character ' * ' each time. Therefore, for a single \( j \) value, 4 asterisks are printed in a row.

Analyzing the Operations Inside the Loops

For every complete iteration of the innermost loop (after printing 4 asterisks), \( System.out.println() \) is called, which moves the cursor to the next line. This happens every time the innermost loop finishes, leading to 3 lines of asterisks being printed for each \( i \), with each line containing 4 asterisks.

Final Output Structure

After completing all iterations for a particular \( i \) value, another \( System.out.println() \) is executed, adding an additional blank line before the next iteration of the \( j \) loop begins under the subsequent iteration of \( i \). This results in the pattern repeating 5 times, each group (block) separated by a blank line.

Determining the Overall Output

Thus, the program prints 5 groups of 3 lines each, where each line contains 4 asterisks ('****'). Between each group is a blank line, creating distinct blocks of text.

Key concepts

For Loop

In Java, a *for loop* is a control structure used for iterating a block of code a fixed number of times. It comprises three parts: initialization, condition, and increment/decrement. The initialization sets a starting point, the condition checks if the loop should continue, and the increment/decrement changes the iteration variable.
A basic example of a for loop is:

• Initialization: int i = 0; sets the starting point of the loop.
• Condition: i < 5; ensures the loop runs only while this is true.
• Increment: i++; increases the loop variable by one each iteration.

For loops are perfect when you know in advance how many times you want the loop to run. In the program segment, the outer for loop starts with i from 1 to 5. This sets the groundwork for the nested loops, coordinating how often the entire block of code will execute.

Control Structures

Control structures like the *for loop* enable developers to dictate the flow of program execution. These are fundamental in Java and include loops, conditionals, and branching mechanisms that together form the backbone of logic handling in programming.
To better understand control structures:

• Loops: Execute a sequence of statements multiple times, until a certain condition is met, like for and while loops.
• Conditionals: if and switch statements allow branching where different code blocks execute based on variable states or conditions.
• Branching: Keywords like break and continue manage and alter the flow of loops directly.

In the provided exercise, multiple nested loops are used within the structure: the outer loop controls the duration of processing, while the inner loops control iterations for detailed operations. This setup allows repetitive tasks to be executed efficiently, creating patterns of output like the one provided.

Java Programming Basics

Understanding *Java programming basics* is essential for any student beginning with this powerful and widely-used language. Java is known for its object-oriented nature, platform independence, and structured syntax, making it a favorite among developers.
Key Java fundamentals include:

• Syntax: The rules defined by Java -- like forcing semicolons at the end of statements -- give clarity and error prevention.
• Data Types: Java supports several data types, including int, boolean, char, and String.
• Control Structures: As seen with loops and conditionals, these structures offer ways to control how your program flows.
• Object-Oriented Principles: Java emphasizes classes and objects as the building blocks of software applications, promoting reusability and manageable code.

By gaining familiarity with these basics, students can write effective programs such as the nested loops exercise above, which involves arraying logical steps to achieve a specified output.