Java Tutorial/Data Type/Wrapper Classes

Autoboxing/unboxing int

class AutoBox {
  public static void main(String args[]) {
    Integer iOb = 100; // autobox an int
    int i = iOb; // auto-unbox
    System.out.println(i + " " + iOb); // displays 100 100
  }
}

Demonstrate a type wrapper.

class Wrap {
  public static void main(String args[]) {
    Integer iOb = new Integer(100);
    int i = iOb.intValue();
    System.out.println(i + " " + iOb); // displays 100 100
  }
}

Primitive Wrappers in detail

For the sake of performance, not everything in Java is an object. There are also primitives, such as int, long, float, double, etc.

java.lang.Integer

1. The java.lang.Integer class wraps an int.
2. The Integer class has two static final fields of type int: MIN_VALUE and MAX_VALUE.
3. MIN_VALUE contains the minimum possible value for an int (-2^31) and
4. MAX_VALUE the maximum possible value for an int (2^31 - 1).

Integer class has two constructors:

public Integer (int value)
     public Integer (String value)

Use Integer constructor to convert int primitive type to Integer object.

public class Main {
  public static void main(String[] args) {
    int i = 10;
    Integer intObj = new Integer(i);
    System.out.println(intObj);
  }
}

Wrapped Class: boolean, int, long

public class WrappedClassApp {
  public static void main(String args[]) {
    Boolean b1 = new Boolean("TRUE");
    Boolean b2 = new Boolean("FALSE");
    System.out.println(b1.toString() + " or " + b2.toString());
    for (int j = 0; j < 16; ++j)
      System.out.print(Character.forDigit(j, 16));
    System.out.println();
    Integer i = new Integer(Integer.parseInt("ef", 16));
    Long l = new Long(Long.parseLong("abcd", 16));
    long m = l.longValue() * i.longValue();
    System.out.println(Long.toString(m, 8));
    System.out.println(Float.MIN_VALUE);
    System.out.println(Double.MAX_VALUE);
  }
}

Wrapper classes for the primitive types

Basic TypeWrapper ClassbyteByteshortShortintIntegerlongLongfloatFloatdoubleDoublebooleanBooleancharCharacter