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

String[] monkey = {"hi", "hi2", "hi3"};
int i = 0;
while (i < monkey.length) {
    System.out.println(monkey[i]);
    i++;
}

hi
hi2
hi3

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 result = new StringBuilder();
        String alphabet = "abcdefghijklmnopqrstuvwxyz";
    
        for (int i = 0; i < phrase.length(); i++) {
            char letter = phrase.charAt(i);
            if (Character.isLetter(letter)) {
                result.append(alphabet.charAt((alphabet.indexOf(letter) + key) % 26));
            }
            else {
                result.append(letter);
            }
        }
        return result.toString();
    }
}

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());

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