Java Academy · Lesson

Nested For & Text Patterns

Use nested for loops to print rectangles, right triangles, and small tables. Control rows (outer) and columns (inner).

Nested For & Text Patterns is a free Java Academy lesson on CoddyKit — lesson 2 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Java Academy learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Nested Concept

Nested loops: a loop inside another loop. Often, the outer loop controls rows and the inner loop controls columns.

Rectangle 3x4

Rectangle 3x4

public class Main {
  public static void main(String[] args) {
    // Outer loop controls the number of rows (3 rows total)
    for (int r = 1; r <= 3; r = r + 1) {
      // Start with an empty string for each row
      String line = "";

      // Inner loop controls the number of columns (4 stars per row)
      for (int c = 1; c <= 4; c = c + 1) {
        // Add one star to the line in each iteration
        line = line + "*";
      }

      // Print the completed line of stars
      System.out.println(line);
    }
  }
}

Right Triangle

Right triangle

public class Main {
  public static void main(String[] args) {
    // Outer loop controls the number of rows (from 1 up to 4)
    for (int r = 1; r <= 4; r = r + 1) {
      // Start with an empty string for each row
      String line = "";

      // Inner loop runs 'r' times, so stars increase with each row
      for (int c = 1; c <= r; c = c + 1) {
        // Add one star to the current line
        line = line + "*";
      }

      // Print the completed line of stars
      System.out.println(line);
    }
  }
}

Right-Aligned

Right-aligned triangle: add spaces before stars.

public class Main {
  public static void main(String[] args) {
    int height = 4; // total number of rows for the triangle

    // Outer loop: controls the row number
    for (int r = 1; r <= height; r = r + 1) {
      String line = "";

      // First inner loop: add spaces so stars are right-aligned
      for (int s = 1; s <= (height - r); s = s + 1) {
        line = line + " ";
      }

      // Second inner loop: add stars according to current row
      for (int c = 1; c <= r; c = c + 1) {
        line = line + "*";
      }

      // Print the final line (spaces + stars)
      System.out.println(line);
    }
  }
}

1..3 Table

Table 1..3

public class Main {
  public static void main(String[] args) {
    // Outer loop controls the rows (1 to 3)
    for (int r = 1; r <= 3; r = r + 1) {
      String line = "";

      // Inner loop controls the columns (1 to 3)
      for (int c = 1; c <= 3; c = c + 1) {
        // Multiply row number (r) by column number (c)
        // Add the result plus a space to the line
        line = line + (r * c) + " ";
      }

      // Print the row after building it
      System.out.println(line);
    }
  }
}

Patterns Demo

Run it: Three patterns printed without any console input.

public class Main {
  public static void main(String[] args) {
    // Rectangle 3x4
    for (int r = 1; r <= 3; r = r + 1) {
      String line = "";
      for (int c = 1; c <= 4; c = c + 1) {
        line = line + "*";
      }
      System.out.println(line);
    }

    // Right triangle
    for (int r = 1; r <= 4; r = r + 1) {
      String line = "";
      for (int c = 1; c <= r; c = c + 1) {
        line = line + "*";
      }
      System.out.println(line);
    }

    // Right-aligned triangle
    int height = 4;
    for (int r = 1; r <= height; r = r + 1) {
      String line = "";
      for (int s = 1; s <= (height - r); s = s + 1) {
        line = line + " ";
      }
      for (int c = 1; c <= r; c = c + 1) {
        line = line + "*";
      }
      System.out.println(line);
    }
  }
}

3x4 Rectangle

Quick check: Which snippet prints a 3x4 rectangle of * (3 rows, 4 columns)?

Recap & Next

Recap: You used nested loops for rectangles, triangles, alignment with spaces, and tiny tables.

Next: Practice and mini-challenges to build confidence with patterns.

Frequently asked questions

Is the “Nested For & Text Patterns” lesson free?

Yes — the full text of “Nested For & Text Patterns” is free to read here on the web, and the Java Academy course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Java Academy course, upgrade to CoddyKit PRO.

What will I learn in “Nested For & Text Patterns”?

Use nested for loops to print rectangles, right triangles, and small tables. Control rows (outer) and columns (inner). You practise Java Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Java Academy?

No prior experience is required. Java Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 3, so you can start here or from the beginning and move at your own pace.

How long does the “Nested For & Text Patterns” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Java Academy lesson?

Yes. Every Java Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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