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 words = "hello";
int i = 0;
while (i < words.length()) {
char c = words.charAt(i);
System.out.println(c);
i++;
}
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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 ch : phrase.toCharArray()) {
if (Character.isLetter(ch)) {
char base = Character.isLowerCase(ch) ? 'a' : 'A';
ch = (char) ((ch - base + key) % 26 + base);
}
encrypted.append(ch);
}
return encrypted.toString();
}
}
// Test cases
CaesarCipher test1 = new CaesarCipher(3, "hello world");
System.out.println("test 1: " + test1.encrypt()); // Expected: khoor zruog
CaesarCipher test2 = new CaesarCipher(10, "abcdefg");
System.out.println("test 2: " + test2.encrypt()); // Expected: lmnopqr
CaesarCipher test3 = new CaesarCipher(-3, "khoor zruog");
System.out.println("test 3: " + test3.encrypt()); // Expected: hello world
test 1: khoor zruog
test 2: klmnopq
test 3: hello world