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:

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);

  }

}

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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());

  }

}

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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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