Wrapper Classes

Java provides wrapper classes for each of the primitive types. The wrapper classes can be used to create objects from the primitive types. These are the wrapper classes for the corresponding primitive types:

Boolean - boolean
Byte - byte
Character - char
Short - short
Integer - int
Long - long
Float - float
Double - double

Boolean

The Boolean class wraps a value of the primitive type boolean in an object.

// Creating a Boolean object
boolean found = true;
Boolean boolObj = Boolean.valueOf ( found );

// Getting back a boolean from a Boolean
boolean aBool = boolObj.booleanValue();

Other methods:

equals ( Boolean obj ) : boolean - Returns true if the Boolean object represents the same boolean value as this object.
toString () : String - Returns a string representation of this Boolean's value.

Character

The Character class wraps a value of the primitive type char in an object.

// Creating a Character object
char ch = 'a';
Character charObj = new Character ( ch );

// Getting a char back from a Character object
char ch2 = charObj.charValue();

Other methods:

compareTo ( Character charObj ) : int - Returns the integer difference between the Unicodes of this character and the other character.
equals ( Character charObj ) : boolean - Returns a boolean true if the two Character objects have the same value.
isDigit ( char ch ) : boolean - Determines if the specified character is a digit.
isLetter ( char ch ) : boolean - Determines if the specified is a letter.
isLetterOrDigit ( char ch ) : boolean - Determines if the specified character is a letter or digit.
isLowerCase ( char ch ) : boolean - Determines if the specified character is a lowercase character.
isUpperCase ( char ch ) : boolean - Determines if the specified character is an uppercase character.
toLowerCase ( char ch ) : char - Converts the character to lowercase.
toUpperCase ( char ch ) : char - Converts the character to uppercase.
toString() : String - Returns a string representing this character's value.

Integer

The Integer class wraps a value of the primitive type int in an object.

// Creating an Integer Object
int x = 10;
Integer xObj = new Integer ( x );

// Get the integer value from an Integer object
int z = xObj.intValue();

Other methods

compareTo ( Integer intObj ) : int - Returns 0 if this Integer is equal to the value of intObj, a value less than 0 if this Integer is less than intObj and a value greater than 0 if this Integer is greater than the value of intObj.
equals (Integer intObj ) : boolean - Returns true if the values of the two Integer objects are the same.
parseInt (String s ) : int - Returns the integer value of the string.
toBinaryString ( int i ) : String - Returns a string representation of the integer in base 2.
toHexString ( int i ) : String - Returns a string representation of the integer in base 16.
toOctalString ( int i ) : String - Returns a string representation of the integer in base 8.
toString () : String - Returns a string representation of the integer.
valueOf ( String s ) : Integer - Returns an Integer object holding the value of the specified string.

Double

The Double class wraps a value of the primitive type double in an object.

// Creating a Double object
double w = 2.512;
Double dObj = new Double ( w );

// Extracting the double value from a Double object.
double v = dObj.doubleValue();

Other Methods

compareTo ( Double d ) : int - Returns 0 if this Double is numerically equal to d, a value less than 0 if this Double is numerically less than d, and a value greater than 0 if this Double is numerically greater than d.
equals ( Double d ) : boolean - Returns true if the two doubles have the same value.
parseDouble ( String s ) : double - Returns a double value represented by the string.
toString() : String - Returns a string representation of this Double object.
valueOf ( String s ) : Double - Returns a Double object holding the double value represented by the string.

Vector

The Vector class implements a growable array of objects. One can access the components using an integer index. But the size of the Vector can grow or shrink. Each Vector object has a capacity and a capacityIncrement. The size of the Vector increases in units of the capacityIncrement.

// Creating a default Vector of capacity 10 and capacityIncrement 0
Vector aVec = new Vector();

// Add object at a specified position in the Vector
aVec.add ( 5, anObj );

// Add object at the end of the Vector
aVec.add ( anObj );

// Remove all the elements in the Vector
aVec.clear();

// Return an object at a specified location
Object anObj = aVec.elementAt ( 5 );

// Test if an object is in the Vector
boolean found = aVec.contains ( anObj );

// Get the index of the first occurence of an element
int x = aVec.indexOf ( anObj );

// Get the index of the last occurence of an element
int x = aVec.lastIndexOf ( anObj );

// Remove an element at a specified position
Object anObj = aVec.remove ( 5 );

// Remove the first occurence of an object
boolean done = aVec.remove ( anObj );

// Replace an element at a specified position in a Vector
Object prevObj = aVec.set ( 5, anObj );

// Get the capacity of the Vector
int capa = aVec.capacity();

// Get the number of elements in a Vector
int num = aVec.size();

// Convert a Vector to an Array
Object[] anArray = aVec.toArray();

// Get a string representation of a Vector containing the String
// representation of each element
String str = aVec.toString();