Each Java primitive data type has a corresponding wrapper class. : Wrapper classes « Utility Classes « SCJP






  1. SCJP
  2. Utility Classes
  3. Wrapper classes
A wrapper class is simply a class that encapsulates a single, immutable value. 

Integer class wraps up an int value
Float class wraps up a float value. 

Primitive           Wrapper Class                   Constructor Arguments

boolean             Boolean                         boolean or String

byte                Byte                            byte or String

char                Character                       char

double              Double                          double or String

float               Float                           float, double, or String

int                 Integer                         int or String

long                Long                            long or String

short               Short                           short or String








8.9.Wrapper classes
8.9.1.Wrapper classes
8.9.2.Wrapper classes and their corresponding primitive variables.
8.9.3.Each Java primitive data type has a corresponding wrapper class.
8.9.4.The Wrapper Constructors
8.9.5.The Character class provides only one constructor, which takes a char as an argument
8.9.6.The constructors for the Boolean wrapper take either a boolean value true or false, or a String.
8.9.7.The valueOf() Methods
8.9.8.Using Wrapper Conversion Utilities
8.9.9.parseXxx() and valueOf()
8.9.10.toString()
8.9.11.Integer and Long provide a toString() method based on a radix.
8.9.12.toXxxString() (Binar y, Hexadecimal, Octal)
8.9.13.autoboxing, auto-unboxing, boxing, and unboxing.
8.9.14.Assignment to wrapper object
8.9.15.Each of the primitive data types has a corresponding wrapper class in the Java standard library.
8.9.16.Integer.parseInt(): convert int to string
8.9.17.Integer.valueOf(String s) returns Integer objects
8.9.18.Integer.MAX_VALUE is the largest value and Integer.MIN_VALUE the smallest that an int primitive can contain.
8.9.19.Wrapper classes can be constructed by passing the value to the appropriate constructor.
8.9.20.Pass into the constructor a String that represents the value to be wrapped.
8.9.21.The values wrapped inside two wrappers of the same type can be checked for equality
8.9.22.After a value has been wrapped, you may eventually need to extract it.
8.9.23.Sometime you need wrapper class
8.9.24.Useful methods from wrapper class
8.9.25.All wrapper classes except Character have a static method called valueOf(String s)
8.9.26.static wrapper methods parseXXX()
8.9.27.Boolean.getBoolean(), Integer.getInteger(), and Long.getLong().
8.9.28.All the wrapper classes provide toString() methods.
8.9.29.Integer and Long classes provide toBinaryString(), toOctalString(), and toHexString() methods
8.9.30.The values All wrapper classes wrap are immutable and Wrapper classes are final.