Object class:
// Although you don't see this
explicitly in most classes,
// every class in Java extends
Object by default.
class Object
{
// Some methods available in Object class:
// - toString()
// - equals(Object obj)
// - hashCode()
// - getClass()
// - clone()
}
Object is a predefined class in Java. It is the root
of the class hierarchy. Every class in Java implicitly extends the Object class if no other superclass is specified
FAQ: What is the superclass of
all classes in Java?
The Object
class is the superclass (also known as the parent or base class) for all
classes in Java.
class A extends Object
{
// Since A doesn't extend any other class,
// it automatically extends Object.
}
class String extends Object {
// String class, like any other class,
// ultimately extends Object.
}
FAQ: What is object class and
when should we use object class?
· indirectly
inherits from the Object class. It is the superclass for
all classes in Java.
· Since Object is the ultimate parent class, it provides several
fundamental methods that are inherited by all Java classes, such as:
- toString(): Returns a string
representation of the object.
- equals(Object obj): Compares the current
object with another object for equality.
- hashCode(): Returns a hash code value
for the object.
- getClass(): Returns the runtime class
of the object.
- clone(): Creates and returns a copy
of the object (if the class implements the Cloneable interface).
- finalize(): Called by the garbage
collector on an object when garbage collection determines that there are
no more references to the object.
Ex:
// An Object reference variable
can store references to any type of object,
// including instances of
Integer, Float, String, etc.
// Example: Storing an int value
in an Object reference variable
Object obj;
// Boxing: Storing an int value
in an Object reference variable
obj = 10; // int value is
automatically boxed into an Integer object
// Boxing: Storing a float value
in an Object reference variable
obj = 10.5f; // float value is
automatically boxed into a Float object
// Storing a String value in an
Object reference variable
obj = "Hello, World!";
an Object reference
variable can store different types of values, including primitive values
through autoboxing:
Explanation
In Java, the Object class
is the root of the class hierarchy. This means that an Object reference variable can refer to
an object of any class, including instances of wrapper classes like Integer, Float, and String.
When you assign a primitive value
to an Object reference, Java
automatically converts the primitive value into its corresponding wrapper class
object through a process called autoboxing.
+-------------------+
+-------------+
| Object ref var |----->|
Integer(10) | (Boxing: int to Integer)
| obj | +-------------+
+-------------------+
|
| +-------------+
|---------------> |
Float(10.5) | (Boxing: float to Float)
| +-------------+
|
| +-------------+
|---------------> | "Hello" | (String is already an object)
+-------------+
·
Storing an int value:
- When you assign an int value like 10 to obj, Java performs autoboxing,
converting the int to an Integer object. Now, obj holds a reference to this Integer object.
·
Storing a float value:
- Similarly, when you assign a
float value like 10.5f to obj, it is autoboxed into a Float object. Now, obj holds a reference to this Float object.
·
Storing a String value:
- When you assign a String value like "Hello" to obj, it directly holds a
reference to the String object, as String is already an object type.
package InterfaceBasics;
public class
TestObjectClassReferenceVariable {
public
static void main(String[] args)
{
int
i= 10;
float
f=10.85f;
//
object ref variable , we can store int value, float value, String value
//
store int value in obj ref variable
Object
oref = i;
// 10
// oref=
10
System.out.println("object
can store int val="+oref);
//
store float value in obj ref var
oref
= f;
// 10.85
// oref =
10.85
System.out.println("object
can store float val="+ oref);
//
store String value in obj ref var
oref
= "Ram";
System.out.println("object
can store String val="+oref);
//
By using Object variable, we can store
any type of value
//when
we want to store any data type val, we will go for Object class.
//
HW store char value in obj ref variable and display it
//
HW store boolean value in obj ref variable and display it
}
}
Object array:
package InterfaceBasics;
public class TestObjectClass {
public
static void main(String[] args)
{
int
a [] = {10,20 ,30};
float
farr[] = {2.4f,3.5f,4.5f};
char
charr [] = {'A','B','C'};
//
Using object arr - 1 int + 1 float +
1 char ....etc
//
define obj arr - store {10, 2.4f,'A',
"Ramu"};
Object
oarr [] = {10 ,2.4f,'A',"Ramu"};
//(or )
//
create object array using new k/w with
size =5
Object
oarr2 [] = new Object [5];// 0 to size-1 i.e o to 5-1=4
//
store 10 value at index no=0
oarr2[0]
= 10;
//
store 2.3f value at index no=1
oarr2[1]
= 2.3f;
//
store 'A' value at index no=2
oarr2[2]
= 'A';
//
store "Ram" value at index
no=3
oarr2[3]
= "Ram";
//
store true value at index no=4
oarr2[4]
= true;
//
get all values from Object array using 2 ways
//
HW 1 . display all values using for loop with index no
//
HW 2 display Object array values using 'for each' loop ?
}
}
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