- Java Introduction
- Java Getting Started
- Java Syntax
- Java Comments
- Java Variables
- Java Data Types
- Java Type Casting
- Java Operators
- Java Strings
- Java Math
- Java Booleans
- Java If ... Else
- Java Switch
- Java While Loop
- Java For Loop
- Java Break And Continue
- Java Arrays
- Java Methods
- Java Method Parameters
- Java Method Overloading
- Java Scope
- Java Recursion
- Java OOP
- Java Classes And Objects
- Java Class Attributes
- Java Class Methods
- Java Constructors
- Java Modifiers
- Java Encapsulation
- Java Packages
- Java Inheritance
- Java Polymorphism
- Java Inner Classes
- Java Abstraction
- Java Interface
- Java Enums
- Java User Input (Scanner)
- Java Date And Time
- Java ArrayList
- Java LinkedList
- Java HashMap
- Java HashSet
- Java Iterator
- Java Wrapper Classes
- Java Exceptions - Try...Catch
- Java Regular Expressions
- Java Threads
- Java Lambda Expressions
- Java Files
- Java Create And Write To Files
- Java Read Files
- Java Delete Files
Java Wrapper Classes
Java Wrapper Classes
Wrapper classes provide a way to use primitive data types (int
, boolean
, etc..) as objects.
The table below shows the primitive type and the equivalent wrapper class:
Primitive Data Type | Wrapper Class |
---|---|
byte | Byte |
short | Short |
int | Integer |
long | Long |
float | Float |
double | Double |
boolean | Boolean |
char | Character |
Sometimes you must use wrapper classes, for example when working with Collection objects, such as ArrayList
, where primitive types cannot be used (the list can only store objects):
Example
ArrayList<int> myNumbers = new ArrayList<int>(); // Invalid
ArrayList<Integer> myNumbers = new ArrayList<Integer>(); // Valid
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Creating Wrapper Objects
To create a wrapper object, use the wrapper class instead of the primitive type. To get the value, you can just print the object:
Example
public class Main {
public static void main(String[] args) {
Integer myInt = 5;
Double myDouble = 5.99;
Character myChar = 'A';
System.out.println(myInt);
System.out.println(myDouble);
System.out.println(myChar);
}
}
Since you're now working with objects, you can use certain methods to get information about the specific object.
For example, the following methods are used to get the value associated with the corresponding wrapper object: intValue()
, byteValue()
, shortValue()
, longValue()
, floatValue()
, doubleValue()
, charValue()
, booleanValue()
.
This example will output the same result as the example above:
Example
public class Main {
public static void main(String[] args) {
Integer myInt = 5;
Double myDouble = 5.99;
Character myChar = 'A';
System.out.println(myInt.intValue());
System.out.println(myDouble.doubleValue());
System.out.println(myChar.charValue());
}
}
Another useful method is the toString()
method, which is used to convert wrapper objects to strings.
In the following example, we convert an Integer
to a String
, and use the length()
method of the String
class to output the length of the "string":
Example
public class Main {
public static void main(String[] args) {
Integer myInt = 100;
String myString = myInt.toString();
System.out.println(myString.length());
}
}
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