Java instantiate Short object in Java

问题

I was wondering why we can do:

Long l = 2L;
Float f = 2f;
Double d = 2d;

or even

Double d = new Double(2);

and not

Short s = 2s; //or whatever letter it could be

nor

Short s = new Short(2); //I know in this case 2 is an int but couldn't it be casted internally or something?

Why do we need to take the constructors either with a String or a short.

回答1:

But you can do this:

Short s = 2;

Or this:

Short s = new Short((short)2);

Or this:

Short s = new Short("2");

Any of the above will work as long as the number is in the range [-2^15, 2^15-1]

回答2:

One of the main rules in Java is that any mathematical operation's result will be stored in a large size variable to avoid truncation. For example if you are adding int with long the result will be long. Hence, any operation on byte, char, or short will result an int even if you added 1 to a byte.There are 2 ways to store the result in the same data type:

a) you do explicit casting:

short s=10;  
s=(short)(s+1);  

b) You can use the auto increment of short hand operations to ask the JVM to do implicit casting:

short s=10;  
s+=21;  

OR

short s=10;  
s++;  

---

if you need short or byte literal, they must be casted as there is no suffix like S or s for short:

byte foo = (byte)100000;
short bar = (short)100000;

来源：https://stackoverflow.com/questions/11526432/java-instantiate-short-object-in-java