Java Wrapper Class

The wrapper classes in Java are used to convert primitive types (int, char, float, etc) into corresponding objects.

Each of the 8 primitive types has corresponding wrapper classes.

Convert Primitive Type to Wrapper Objects

We can also use the valueOf() method to convert primitive types into corresponding objects.

Example 1: Primitive Types to Wrapper Objects

class Main {
  public static void main(String[] args) {

    // create primitive types
    int a = 5;
    double b = 5.65;

    //converts into wrapper objects
    Integer aObj = Integer.valueOf(a);
    Double bObj = Double.valueOf(b);

    if(aObj instanceof Integer) {
      System.out.println("An object of Integer is created.");
    }

    if(bObj instanceof Double) {
      System.out.println("An object of Double is created.");
    }
  }
}

Output

An object of Integer is created.
An object of Double is created.

In the above example, we have used the valueOf() method to convert the primitive types into objects.

Here, we have used the instanceof operator to check whether the generated objects are of Integer or Double type or not.

However, the Java compiler can directly convert the primitive types into corresponding objects. For example,

int a = 5;
// converts into object
Integer aObj = a;

double b = 5.6;
// converts into object
Double bObj = b;

This process is known as auto-boxing. To learn more, visit Java autoboxing and unboxing.

Note: We can also convert primitive types into wrapper objects using Wrapper class constructors. But the use of constructors is discarded after Java 9.

Wrapper Objects into Primitive Types

To convert objects into the primitive types, we can use the corresponding value methods (intValue(), doubleValue(), etc) present in each wrapper class.

Example 2: Wrapper Objects into Primitive Types

class Main {
  public static void main(String[] args) {

    // creates objects of wrapper class
    Integer aObj = Integer.valueOf(23);
    Double bObj = Double.valueOf(5.55);

    // converts into primitive types
    int a = aObj.intValue();
    double b = bObj.doubleValue();

    System.out.println("The value of a: " + a);
    System.out.println("The value of b: " + b);
  }
}

Output

The value of a: 23
The value of b: 5.55

In the above example, we have used the intValue() and doubleValue() method to convert the Integer and Double objects into corresponding primitive types.

However, the Java compiler can automatically convert objects into corresponding primitive types. For example,

Integer aObj = Integer.valueOf(2);
// converts into int type
int a = aObj;

Double bObj = Double.valueOf(5.55);
// converts into double type
double b = bObj;

This process is known as unboxing.

Advantages of Wrapper Classes

• In Java, sometimes we might need to use objects instead of primitive data types. For example, while working with collections.

  // error
  ArrayList<int> list = new ArrayList<>();
  
  // runs perfectly
  ArrayList<Integer> list = new ArrayList<>();

  In such cases, wrapper classes help us to use primitive data types as objects.
• We can store the null value in wrapper objects. For example,

  
  // generates an error
  int a = null;
  
  // runs perfectly
  Integer a = null;
  

Note: Primitive types are more efficient than corresponding objects. Hence, when efficiency is the requirement, it is always recommended primitive types.