1. char is for storing single characters
char and String
char is for storing single characters
primitive type
constants: a printable character enclosed in single quotes
( ‘Y’ ‘y’ ‘#’ ‘7’ )
char widens to int, long, float or double
operators: ++ and --
caution: (char)7 is not the same as ‘7’
String is for storing a sequence of characters
built-in Java class
constants: zero or more characters enclosed in double quotes
a String object is ______________
operators: +
caution: new not used with constant notation.
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2. Examples variable declarations private char initial, digit;
private String name, message, str;
initial = ‘D’;
digit = ‘0’;
digit++;
initial = (char)(initial + 3);
System.out.println(digit);
System.out.println(initial);
name = “Riley”;
str = “”;
message = name + “ assigns programs.”;
System.out.println( initial + “. “ + message );
System.out.println( “digit value is “ + digit );
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3. Class Diagram String «constructor» «query» «translate»
+ String( String )
. . .
«query»
+ char charAt( int )
+ int length()
+ int substring(int)
+ int substring(int, int)
«translate»
+ String toLowerCase( )
+ String toUpperCase( )
«infix operator» +
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4. Examples variable declarations private String cheese, theory;
cheese = “limburger”;
System.out.println( cheese.substring(3) );
cheese = cheese.substring(6);
SYstem.out.println( cheese );
cheese = “gouda”.substring(2);
System.out.println( cheese );
theory = “quantum mechanics”;
System.out.println( theory.substring(4,10));
System.out.println( theory );
theory = “hadrons”;
System.out.println( cheese.substring(3,5)
+ “ “ + theory.charAt(0)
+ cheese.substring(4)
+ ‘t’ );
Output: burger …. ger … uda … tum me … quantum mechanics … da hat
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5. Differences Between Types
Strings and primitive types are largely incompatible...
• You can add, subtract, multiply or divide most primitives, but not Strings
String product = "75.2" * "3";
• You easily extract individual characters from Strings, but not primitives
char decimalPoint = ("38.25").charAt(2);
char nonSymbol = (38.25).charAt(2);
• Because they are a reference type, Strings are instantiated via new, but not
primitives.
char letter = new char('D');
• Even if a String stores a single character it is incompatible with char.
char questionMark = "?";
String asterisk = '*';
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6. Type Conversion Expressions
Any primitive  String
concatenate to the empty string
String realValue = "";
String logicalNegative = false + "";
String  char
use charAt
char initial = ("7").charAt(0);
String  Any primitive excepting char
1) Instantiate Scanner passing the String to be converted 2) Call nextType() upon this Scanner object.
Note that the Scanner abbreviation line replaces the last two lines and eliminates the need for a Scanner variable.
The caution means that the String used to create the Scanner must represent a valid Double constant. (This is true for any of the nextType() methods.)
String closeToPi = " ";
Scanner converter = new Scanner(closeToPi);
double approximationOfPi = converter.nextDouble();
which can be abbreviated...
double approximationOfPi =
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7. Enumerated Types
An enumerated type is a user-defined type with its own constants.
The constants are identifiers.
enum FlippingCoin {heads, tails}
. . .
FlippingCoin flipper;
flipper = FlippingCoin.tails;
Every enumerated type includes two conversion methods:
ordinal() returns an int (0 for first, 1 for second, and so forth)
name() returns an String from the identifier
flipper = FlippingCoin.tails;
int flipNum = flipper.ordinal();
String flipName = flipper.name();
// assert:
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8. Internal or External Declaration?
Enumerated types may either
be declared within a class or
in a separate file ...but not
local to a method.
public class Driver {
private enum Planets
{ mercury, venus, earth, mars,
jupiter, saturn, uranus,
neptune, pluto }
private Planets favoritePlanet;
public Driver() {
. . .
favoritePlanet = earth; }
public enum Planets {
mercury, venus, earth, mars,
jupiter, saturn, uranus,
neptune, pluto }
public class Driver {
private Planets favoritePlanet;
public Driver() {
. . .
favoritePlanet = Planets.earth; }
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9. Q: Why use enumerated types?
A: Safety
favoritePlanet = -33; is permitted using the int version.
Using enumerated...
Using int...
public class Driver {
private enum Planets
{ mercury, venus, earth, mars,
jupiter, saturn, uranus,
neptune, pluto }
private Planets favoritePlanet;
public Driver() {
. . .
favoritePlanet = earth; }
public class Driver {
private int favoritePlanet;
private final int mercury = 0;
private final int venus = 1;
private final int earth = 2;
private final int mars = 3;
private final int jupiter = 4;
private final int saturn = 5;
private final int uranus = 6;
private final int pluto = 7;
public Driver() {
. . .
favoritePlanet = earth; }
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