4.3 String Iteration

simple for loop to iterate through every character using index with charAt():

String word = "hello";
for (int i = 0; i < word.length(); i++) {
    System.out.println(word.charAt(i));
}

in order to use an enhanced for loop, a character array is needed.
toCharArray() can help accomplish this.
example of iteration with an enhanced for loop:

String word = "hello";
for (char c : word.toCharArray()) {
    System.out.println(c);
}

Popcorn Hack:

Iterate through the characters a string with a while loop

public class WhileLoopString {
    public static void main(String[] args) {
        String str = "Hello world!";
        
        int index = 0;

        while (index < str.length()) {
            char currentChar = str.charAt(index);
            System.out.println("Character at index " + index + ": " + currentChar);
            index++;
        }
    }
}

WhileLoopString.main(null);

Character at index 0: H
Character at index 1: e
Character at index 2: l
Character at index 3: l
Character at index 4: o
Character at index 5:  
Character at index 6: w
Character at index 7: o
Character at index 8: r
Character at index 9: l
Character at index 10: d
Character at index 11: !

What is a substring?

  • a substring is a subset of the main string
  • the substring(a,b) method creates a substring with the characters of the original string with indices of a to b.
  • string.length() returns the length of the string
  • string1.equals(string2) determines if the two strings have the same characters
String word = "sunflower";
String sub = "low";
boolean found = false;
for (int i = 0; i < word.length(); i++) {
    String portion = word.substring(i, i+sub.length());
    if (portion.equals(sub)){
        found = true;
    }
}

System.out.println("is " + )

Iterating through words

use split() to split a string into an array.
then we can iterate through the array to access each individual word

String phrase = "this is a string";
String[] words = phrase.split(" ");
for (String word : words) {
    System.out.println(word);
}

Homework Hack!

code a caesar cipher that will encrypt any string with any key provided.
your code should go into the encrypt() method, and should successfully pass the test cases provided
as a bonus, try to use StringBuilder

public class CaesarCipher {
    private int key;
    private String phrase;

    public CaesarCipher(int key, String phrase) {
        this.key = key;
        this.phrase = phrase;
    }

    public String encrypt() {
        StringBuilder encrypted = new StringBuilder();
        for (char c : phrase.toCharArray()) {
            if (Character.isLetter(c)) {
                char base = Character.isLowerCase(c) ? 'a' : 'A';
                encrypted.append((char) ((c - base + key) % 26 + base));
            } else {
                encrypted.append(c); // keep non-letters the same
            }
        }
        return encrypted.toString();
    }

    public static void main(String[] args) {
        CaesarCipher test1 = new CaesarCipher(3, "hello world");
        CaesarCipher test2 = new CaesarCipher(10, "abcdefg");
        CaesarCipher test3 = new CaesarCipher(20, "i love csa");

        System.out.println("test 1: " + test1.encrypt());
        System.out.println("test 2: " + test2.encrypt());
        System.out.println("test 3: " + test3.encrypt());
    }
}


CaesarCipher.main(null);

test 1: khoor zruog
test 2: klmnopq
test 3: c fipy wmu
2
15


Iteration: 0

Current Velocity: 2, 2