# Type Wrappers (Wrapper Class)
###### tags: `Java` `Basic Java`

## What is Type Wrappers?
1. A way or method to turn all the 8 primitive data types (boolean , byte , char , short , int , long , float and double) into classes. Thus, they become **reference data types**.

2. Since they are now classes, which means that we could invoke some methods written inside each classes.

## How to Wrap a Type?　-- take Integer as an example
1. Manual Boxing: primitive type -> reference type
* ~~public Integer (int value): through constructor~~(Removal Usage, not recommended)
* **public static Integer valueOf(int i): through static method**

        int num = 10;
        
        Integer i1 = Integer.valueOf(num);
        System.out.println(i1);

> output result: 10

2. Manual Unboxing: reference type -> primitive type

        int i = i1.intValue();
        System.out.println(i);

> output result: 10

3. Auto boxing & Auto Unboxing: (JDK 5 afterwards)

        int num = 10;

        // Auto Boxing
        Integer i1 = num;

        // Auto Unboxing
        int i = i1;

        System.out.println(i1);
        System.out.println(i);

> output result: 10 10

## Frequently Used Method

1. public static String toBinaryString(int i):Decimal to Binary
2. public static String toOctalString(int i): Decimal to Octal
3. public static String toHexString(int i): Decimal to Hex
4. public static int parseInt(String s): String to Integer

        int num = 999;

        String s1 = Integer.toBinaryString(num);
        String s2 = Integer.toOctalString(num);
        String s3 = Integer.toHexString(num);

        System.out.println(s1);
        System.out.println(s2);
        System.out.println(s3);

>Output Result:
>1111100111
>1747
>3e7

        String s = "123";
        System.out.println(Integer.parseInt(s) + 100);

>Output Result: 223 (not 123100)

Practice

        String str = "10,50,30,20,40";

        String[] strArray = str.split(",");

        int[] intArray = new int[strArray.length];

        for (int i = 0; i < strArray.length; i++) {
            intArray[i] = Integer.parseInt(strArray[i]);
        }

        for (int i = 0; i < intArray.length; i++) {
            System.out.print(intArray[i] + "\t");
        }

> 10 50 30 20 40