Question

Write an application that displays the following patterns separately, one below the other. Use for loops to generate the patterns. All asterisks (*) should be printed by a single statement of the form System.out.print( '*' ); which causes the asterisks to print side by side. A statement of the form System.out.println(); can be used to move to the next line. A statement of the form System.out.print( ' ' ); can be used to display a space for the last two patterns. There should be no other output statements in the program. [Hint: The last two patterns require that each line begin with an appropriate number of blank spaces.]

Short answer

Use nested loops to print four different triangle patterns with increasing and decreasing asterisks, applying spaces for alignment.

Step-by-step solution

Initialize Variables

Begin by setting the maximum number of rows for the patterns. For example, use an integer variable `rows` to store the number of rows for each pattern, like `int rows = 5;`. This value can be adjusted to change the size of the patterns.

First Pattern - Right Triangle

Use a double `for` loop to create a right triangle pattern. The outer loop iterates over the number of rows, and the inner loop prints the corresponding number of asterisks for that row. For example: ```java for (int i = 1; i <= rows; i++) { for (int j = 1; j <= i; j++) { System.out.print('*'); } System.out.println(); } ```

Second Pattern - Inverted Right Triangle

Create an inverted right triangle using a similar double `for` loop structure. This time, the outer loop iterates from `rows` down to 1, and the inner loop prints decreasing numbers of asterisks: ```java for (int i = rows; i >= 1; i--) { for (int j = 1; j <= i; j++) { System.out.print('*'); } System.out.println(); } ```

Third Pattern - Right-Aligned Triangle

For the right-aligned triangle, start each line with a number of spaces before the asterisks. Use the double `for` loop, with the first inner loop for spaces and the second for asterisks: ```java for (int i = 1; i <= rows; i++) { for (int j = 1; j <= rows - i; j++) { System.out.print(' '); } for (int k = 1; k <= i; k++) { System.out.print('*'); } System.out.println(); } ```

Fourth Pattern - Left-Aligned Inverted Triangle

Like the previous step, start with spaces but decrease the number of asterisks per line, aligning the pattern to the left: ```java for (int i = rows; i >= 1; i--) { for (int j = 1; j <= rows - i; j++) { System.out.print(' '); } for (int k = 1; k <= i; k++) { System.out.print('*'); } System.out.println(); } ```

Compile and Run the Program

Compile the Java program using `javac` and run it using `java` to see the patterns printed on the console: ```shell javac PatternPrinter.java java PatternPrinter ```

Key concepts

for loop in Java

In Java programming, a 'for loop' is one of the most commonly used control structures. It is especially useful when you need to repeat a set of statements a specific number of times.
A basic for loop in Java follows this structure:

• Initialization: Set a variable to start the loop.
• Condition: A logical test that must be true for the loop to continue.
• Increment/Decrement: Adjusts the variable on each loop iteration.

Here is an example that loops through a sequence from 1 to 5: ```java for (int i = 1; i <= 5; i++) { System.out.println(i); } ``` This loop runs five times, printing numbers from 1 to 5, incrementing by one each cycle. The flexibility in a for loop allows it to be tailored to a wide variety of scenarios, such as generating patterns or processing arrays.

control structures

Control structures in Java are essential components that control the flow of execution of code. They allow developers to dictate the path that the program should take based on different conditions.
Java provides several control structures:

• Loops: Execute a block of code repeatedly (e.g., for, while, do-while).
• Decision-making: Conditional paths using if, if-else, switch statements.
• Branching: Change the flow using break, continue, and return statements.

In our case of pattern printing, 'for loops' are used to manage the number of iterations, whereas the structure itself provides a clear and concise way to define both simple and complex repetitive tasks. Understanding control structures is vital for grasping program logic and creating efficient solutions.

patterns in Java

Working with patterns in Java is a great exercise to strengthen understanding of loops and logic. Patterns are a visual output, often using special characters like asterisks or numbers, arranged in a specific order such as triangles or pyramids.
Creating patterns involves:

• Defining the number of lines you wish to display, usually with a variable like `rows`.
• Using nested for loops where the outer loop dictates the number of lines and the inner loop manages the content of each line, like asterisks.
• Including special conditions for spaces or line shifts to achieve alignment and shape.

For example, in the right triangle pattern, each line adds an additional asterisk to the previous one. Patterns are both fun and challenging, offering plenty of opportunities to experiment with and visualize the power of loops.

Java basics

Java Basics refer to the foundational elements of programming with Java, encompassing syntax, data types, loops, and basic control flow. To begin with Java, it's important to understand:

• Syntax: Java's structure follows a strict syntax including semi-colons to end statements and braces for blocks.
• Data Types: Such as int, double, char, string, which define what kind of data a variable can store.
• Control Structures: Such as loops and conditional statements that direct the flow of the program.
• Input/Output: Most commonly via console using System.out for output and Scanner for input.

Starting with Java requires installing the Java Development Kit (JDK) and setting up an Integrated Development Environment (IDE). The strong typing and object-oriented nature make Java both powerful and flexible for developing applications. Understanding these fundamentals enables you to build effective and efficient Java applications.