String and Scanner

CS 21a: Introduction to Computing I

First Semester, 2013-2014

The String Class►String: a built-in class in Java►Methods on String objects:

► public int length()► public String toUpperCase()► public String substring( int first, int last )

► javap java.lang.String for a complete list► Note: strings are immutable (no mutator

methods)►String objects have a special treatment in

Java► To enable string literals, string display, and

string concatenation

Using Strings

►String literal example: "Hello, World"►String variable:String message = "Hey";// same as String message = new String("Hey");

►Using strings:println( "Hello, World" );println( message );println( message.length() );String caps = message.toUpperCase();println( caps );

Prints:Hello,

WorldHey3HEY

Strings are Objects

►String variables contain object references

String s = "Hey";

►Calling length on a stringint x = s.length();

s

"Hey"

length()"Hey"3

Strings are Objects

►Calling toUpperCase on a string returns another stringString caps = s.toUpperCase();

►Note that the state of s does not change in this case

toUpperCase()

"Hey""HEY"

String Concatenation

►The + operator causes a concatenation if the operands are stringsprintln( "basket" + "ball" );

► If only one operand is a string, the other operand is first converted to a string and then a concatenation is performedint ans = 5;println( "The answer is " + ans );

Prints:basketbal

l

Prints:The answer is 5

Converting betweenStrings and Number Types

►Supposeint i = 5; double d = 10.0; String s = "7";

►From String to numberi = Integer.parseInt( s ); // assigns 7 to i

d = Double.parseDouble( s ); // assigns 7.0 to d

►From number to Strings = Integer.toString( i ); // assigns "5" to s

s = Double.toString( d ); // assigns "10.0" to s

► Can also use concatenations = "" + d;

The substring Method► Each character in a String object has a position

(starting with 0)► The parameters for substring indicate:

► first: the starting letter of the substring of interest► last: the position following the ending letter of the

substring► This way, (last-first) = the length of the resulting

substring► Example:String s = "Ateneo de Manila";String a = s.substring( 0, 6 ); // "Ateneo"String b = s.substring( 6, 9 ); // " de"String c = s.substring( 10,16 ); // "Manila"

Reading Console Inputand the Scanner Class

► To enable console input:► Before the declaration of the application class, type:

import java.util.Scanner;► At the beginning of the main method of the Java

application, create a scanner object:Scanner in = new Scanner( System.in );

► Then, invoke methods on the Scanner objectint i = in.nextInt();

double d = in.nextDouble();

String s = in.nextLine(); // reads an entire line of input

String w = in.next(); // reads one word only

Input Exampleimport java.util.Scanner;public class DollarToPesoConversion{ public static void main( String args[] ) { Scanner in = new Scanner( System.in ); System.out.print( "Type dollar amount: " ); double dollars = in.nextDouble(); System.out.print( "Conversion rate: " ); double rate = in.nextDouble(); System.out.print( "Pesos:" ); System.out.println( dollars*rate ); }}

Practice Programming Problem

►Write a program that reads one name from console and says hello to it.

►Sample InputJustin Bieber

►Sample OutputHello, Justin Bieber!