Chapter 6b - For Loops

Introducing For Loops

import java.util.*;
class Main {
  public static void main(String[] args) {
    for(int i = 1; i<3; i++){
      System.out.println(i);
    }
    
  }
}

note

Animation extracted from Quora

👀

Placing Tables

import java.util.*;
// https://www.geeksforgeeks.org/java-for-loop-with-examples/
class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    // a simulation of setting the table
    System.out.println("Enter number of table placements to be set");
    int n = sc.nextInt();
    sc.close();
    int i;
    for(i = 1; i<=n; i++){
      System.out.println("Plate placed");
      System.out.println("Silverware placed");
      System.out.println("Napkin placed");
      System.out.println("Glass of water placed");
      System.out.println("Table has been set for " + i);
      System.out.println();
    }
    System.out.println("It's dinner time!");
  }
}

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Try it: for loops

Quiz

For loops

1 / 2

for (int i = 0; i < 5; i++) { ... } — how many times does the body run?

for (int i = 0; i < 5; i++) { ... }

Pick an answer to see if you are right.

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Chapter summary

Key takeaways

1. for (init; condition; update) bundles a loop's setup, its stopping condition, and its per-pass update into one line — reach for it whenever you already know the number of repetitions (or can compute it).
2. The init runs once; then Java repeatedly checks condition, runs the body, and runs update, in that order, until condition is false.
3. A for loop is usually the clearer choice when counting up or down over a known range; a while loop is usually clearer when you are waiting for something to happen (like valid input).
4. Nesting a for loop inside another is exactly how you build grids, tables, and patterns — covered in the next chapter.

Exercises

Activity: Print evens

Read an integer n. Print every even number from 2 up to n (inclusive), one per line, using a for loop.