String is a class, and a value of type String is an object. That object contains data, namely the sequence of characters that make up the string. It also contains subroutines. All of these subroutines are in fact functions.
Stringadvice;advice ="Seize the day!";
System.out.print("The number of characters in ");System.out.print("the string \"Hello World\" is ");System.out.println("Hello World".length());
String is not a primitive type, but a class/type
String variables store references to memory addresses
Strings are immutable! That is, you cannot change a string, but you can assign a new string to a variable.
A string cannot span more than one line
Java escape sequence
String is a sequence of (unicode) characters
When we declare a variable of type String, it does not create an object. String founder;
public class EnumDemo {
// Define two enum types -- remember that the definitions
// go OUTSIDE the main() routine!
enum Day { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY }
enum Month { JAN, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC }
public static void main(String[] args) {
Day tgif; // Declare a variable of type Day.
Month libra; // Declare a variable of type Month.
tgif = Day.FRIDAY; // Assign a value of type Day to tgif.
libra = Month.OCT; // Assign a value of type Month to libra.
System.out.print("My sign is libra, since I was born in ");
System.out.println(libra); // Output value will be: OCT
System.out.print("That's the ");
System.out.print( libra.ordinal() );
System.out.println("-th month of the year.");
System.out.println(" (Counting from 0, of course!)");
System.out.print("Isn't it nice to get to ");
System.out.println(tgif); // Output value will be: FRIDAY
System.out.println( tgif + " is the " + tgif.ordinal()
+ "-th day of the week.");
}
}
String poem = """
As I was walking down the stair,
I met a man who wasn't there.
He wasn't there again today.
I wish, I wish he'd go away!""";
String poem = "As I was walking down the stair,\n"
+ " I met a man who wasn't there.\n"
+ "He wasn't there again today.\n"
+ " I wish, I wish he'd go away!\n";
import java.util.Scanner;
public class LetterCounter1 {
// Asks the user for a message and then prints the
// number of times each letter appears in the message
public static void main(String[] args) {
String alphabet = "abcdefghijklmnopqrstuvwxyz";
// or String alphabet = new String("abcdefghijklmnopqrstuvwxyz");
System.out.println("Enter a message.");
// Get the input from the user using Scanner
Scanner keyboard = new Scanner(System.in);
String message = keyboard.nextLine().toLowerCase();
// loop through each letter in the alphabet
// and print the count of it in message
for (int i = 0; i < 26; i++) {
char letter = alphabet.charAt(i);
int numLetters = count(letter, message);
if (numLetters > 0) {
System.out.println(letter + " " + numLetters);
}
}
}
// Returns the number of times ch occurs in the text
public static int count(char ch, String text) {
// loop through each character in the message
// and see if it is the same as ch
int counter = 0;
for (int i = 0; i < text.length(); i++) {
if (text.charAt(i) == ch) {
counter++;
}
}
return counter;
}
}
# Asks the user for a message and then prints the
# number of times each letter appears in the message
def letter_counter():
alphabet = "abcdefghijklmnopqrstuvwxyz"
message = input("Enter a message.\n")
for i in range(26):
letter = alphabet[i]
numLetters = count(letter, message)
if numLetters > 0:
print(letter + " " + str(numLetters))
def count(ch, text):
counter = 0
for i in range(len(text)):
if text[i] == ch:
counter = counter + 1
return counter
letter_counter()
public class StringDemo {
public static void main(String[] args) {
String s = "a";
System.out.println("s = \""+ s + "\"");
System.out.println("s.length: " + s.length());
System.out.println();
s = "ab";
System.out.println("s = \""+ s + "\"");
System.out.println(" s.charAt(0): " + s.charAt(0));
System.out.println(" (int)s.charAt(0): " + (int)s.charAt(0));
System.out.println(" s.length: " + s.length());
System.out.println();
s = "";
System.out.println("s = \""+ s + "\"");
System.out.println(" s.length: " + s.length());
System.out.print(" s.length == 0 ");
System.out.println(s.length() == 0);
System.out.print(" s == null ");
System.out.println(s == null);
System.out.println();
s = null;
System.out.println(" s = null ");
System.out.print(" s == null ");
System.out.println(s == null);
//System.out.print("s.length: " );
//System.out.println(s.length());
//int i = null;
System.out.println();
s = "hello world";
System.out.println("s = \""+ s + "\"\ns.contains(\"lo\":) ");
System.out.println(s.contains("lo"));
System.out.println();
// comparisons
System.out.println("compareTo: ");
System.out.println("word vs work " + "word".compareTo("work"));
System.out.println("word vs words " + "word".compareTo("words"));
System.out.println("word vs wor " + "word".compareTo("wor"));
System.out.println("word equals work " + "word".equals("work"));
System.out.println();
// equality
String ab = "ab";
String cd = "cd";
String s1 = "abcd";
String s2 = ab + cd;
String s3 = "ab" + "cd";
String s4 = "ab".concat("cd");
// Note that s1, s2, s3, and s4 all hold the characters "abcd"
System.out.println("See how equals works as expected for ALL of them:");
System.out.println(s1.equals(s2));
System.out.println(s1.equals(s3));
System.out.println(s1.equals(s4));
System.out.println();
System.out.println("But == only works as expected for SOME of them:");
System.out.println(s1 == s2);
System.out.println(s1 == s3);
System.out.println(s1 == s4);
// Moral of the story: Do NOT use "==" with Strings -- the results are unpredictable!
System.out.println();
// a pattern using concat to build a result string
// CAUTION - do NOT use if you're constructing a LOT of Strings!
// Once we start using Objects, I will show you a better way...
String result = "";
for (int i = 0; i < 10; i++) {
result += "Margaret";
}
System.out.println(result);
}
}
