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Why use int instead of Integer (or the other way around) in Java? [duplicate]

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When to use wrapper class and primitive type
(11 answers)
What is the difference between Integer and int in Java?
(11 answers)
Closed 1 year ago.
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I know that Integer is a class and int is just a number, but when should we use one over another and how to convert Integer to int (and vice versa)?
** Also, there is this
question (what is autoboxing by the way) but I am asking WHEN to use int over Integer in actual programming (such as performance issues, ease of use and readability) and vice versa and not the DIFFERENCE between them.

Why do we create object variables like this? [duplicate]

This question already has answers here:
Differences between new Integer(123), Integer.valueOf(123) and just 123
(6 answers)
create a new Integer object that holds the value 1?
(2 answers)
Advantage of using new Integer(a) over a
(3 answers)
using new(Integer) versus an int
(3 answers)
Closed 3 years ago.
I am new to learning Java, and I was told to create object variables like this:
Integer a = new Integer(2);
Instead of like this:
Integer a = 2;
Can someone explain why is creating object variables the 2nd way bad?
edit: I am adding this here cause I am getting mixed answers
Which one am I supposed to use and when?

The second approach is actually better, since it will implicitly call Integer.valueOf(). From the docs:
Returns an Integer instance representing the specified int value. If a new Integer instance is not required, this method should generally be used in preference to the constructor Integer(int), as this method is likely to yield significantly better space and time performance by caching frequently requested values. This method will always cache values in the range -128 to 127, inclusive, and may cache other values outside of this range.
(Emphasis mine.)
See also: Autoboxing

How to set sth. on infinity in Java? [duplicate]

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How to implement infinity in Java?
(11 answers)
Closed 5 years ago.
I want to implement the dijkstra algorithm and have to set each note at the beginning to infinity.
I would like to know, if there is any function in Java which makes it easy.

Double.POSITIVE_INFINITY if you are using Double to store your data.
Also note that this is not a number, which is nice depending on what you want to do. Double supports this concept.

Java Newbie - When to use it? Relating to Boxing/Unboxing I think [duplicate]

This question already has answers here:
Which is better: letting Java do autoboxing or using valueOf()
(3 answers)
Closed 6 years ago.
Integer x = 5;
Integer x = Integer.valueOf(5);
Is there any scenario where I would want to use the 2nd one specifically or is it redundant altogether and shouldn't not bother about it?

After Java 5 (because of autoboxing / unboxing) there is no difference except the first one is shorter.

Both statements are equivalent.
The statement Integer x = 5 would be compiled to
Integer x = Integer.valueOf(5);
The compiler will do that for you behind the scene, so the only difference is the number of character in source file.

Integer - toString() function [duplicate]

This question already has answers here:
How to convert number to words in java
(31 answers)
Int to English words in Java
(4 answers)
Closed 9 years ago.
I search but cannot find on the web.
Is there a function that can represent any integer into its String litteral representation ?
Example :
Integer i1 = new Integer(4);
Integer i2 = new Integer(30);
i1.callSomeFunction();
i2.callSomeFunction();
Output :
"Four"
"Thirty"
If you know another function which isn't in the Integer class, it's fine too.

There is no standard method to do this but take a look at this. There is an example for a number to words in the English language converter.