M.Moi M.Moi - 1 year ago 77
Java Question

Java - Objects and variables confused

I am confused between these three codes

int a = 5;
int b = 6;
int c = 5;


Integer x = new Integer(5);
Integer y = new Integer(6);
Integer z = new Integer(5);


Integer i = 5;
Integer j = 6;
Integer k = 5;

I know that the first one are some variables that contain values

and the second one are some variables reference to some different objects

but what is the third one !! I know that they are Referenced data types

but i can't understand why and how many objects created .. if any!

Answer Source

Integer is a (wrapper) class name and so the variables of this type are objects. When x is assigned the value of new Integer(5) then, ethically, you cannot use x directly for mathematical operations. To use x in operations, you have to use the wrapper class method intValue() to get x's value in numeric (primitive) form from object form.


Integer x = new Integer(5);
int my_x = x.intValue();
int y = 10 + my_x; //y = 15  

However, using x directly in mathematical ops would not produce an error and, in fact, will produce the same output as going through the above step will. This is because the JVM implicitly converts the object to primitive data value and this process is called Auto boxing. The inverse, when implicitly done, is called Un-boxing. Therefore, in the above example, you can also do this:

Integer x = new Integer(5);
int y = 10 + x; //y = 15;

Hope you now understand.

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