Strings - Java

STRINGS

^—    string: An object storing a sequence of text characters.

^—    Unlike most other objects, a String is not created with new. String name = "text";

String name = expression;

^—    Examples:

String          name =       "Marla        Singer";

int               x        =       3;

int               y        =       5;

String point = "(" + x + ", " + y + ")";

Indexes

^—    Characters of a string are numbered with 0-based indexes: String name = "P. Diddy";

^—    The first character's index is always 0

^—    The last character's index is 1 less than the string's length

^—    The individual characters are values of type char (seen later)

String methods

//        index 012345678901

String s1     = "Stuart Reges";          

String s2     = "Marty Stepp";          

System.out.println(s1.length());        // 12

System.out.println(s1.indexOf("e"));                   // 8

System.out.println(s1.substring(7, 10))      // "Reg"

String s3     = s2.substring(2, 8);               

System.out.println(s3.toLowerCase());      // "rty st"

ï‚—       Given the following string:

//        index 0123456789012345678901 String book = "Building Java Programs";

ï‚—       How would you extract the word "Java" ?

ï‚—       How would you extract the first word from any string?

Modifying strings

^—   Methods like substring, toLowerCase, etc. create/return

a new string, rather than modifying the current string.

String s = "lil bow wow";

s.toUpperCase();

System.out.println(s);  // lil bow wow

^—    To modify a variable, you must reassign it: String s = "lil bow wow";

s = s.toUpperCase();

System.out.println(s); // LIL BOW WOW

Strings as parameters

public class StringParameters {

public static void main(String[] args) { sayHello("Marty");

String teacher = "Helene"; sayHello(teacher);

}

public static void sayHello(String name) { System.out.println("Welcome, " + name);

}

}

Output:

Welcome, Marty

Welcome, Helene

Strings as user input

^—    Scanner's next method reads a word of input as a String. Scanner console = new Scanner(System.in); System.out.print("What is your name? ");

String name = console.next(); name = name.toUpperCase();

System.out.println(name + " has " + name.length() +

" letters and starts with " + name.substring(0, 1)); Output:

What is your name? Madonna MADONNA has 7 letters and starts with M

^—    The nextLine method reads a line of input as a String.

System.out.print("What is your address? ");

String address = console.nextLine();

Comparing strings

^—    Relational operators such as < and == fail on objects. Scanner console = new Scanner(System.in); System.out.print("What is your name? ");

String name = console.next(); if (name == "Barney") {

System.out.println("I love you, you love me,"); System.out.println("We're a happy family!");

}

^—    This code will compile, but it will not print the song.

^—    == compares objects by references (seen later), so it often gives false even when two Strings have the same letters.

The equals method

^—    Objects are compared using a method named equals. Scanner console = new Scanner(System.in); System.out.print("What is your name? ");

String name = console.next(); if (name.equals("Barney")) {

System.out.println("I love you, you love me,"); System.out.println("We're a happy family!");

}

^—   Technically this is a method that returns a value of type boolean, the type used in logical tests.