The difference between final and static final-modified constants in Java

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Final: Used to modify classes, variables, methods:

The final decorated class cannot have subclasses, nor can it be inherited.

The final modified variable is a constant and cannot be re-assigned.

The final decorated method cannot be overridden

The difference between the final modified constant ① and the static final-modified constant ② is now explained.

For example:

①final long Current_time=system.currentmillis ();

②static final long Current_time=system.currentmillis ();

Do not use static adornments:

If you assign a fixed value directly to a constant, the value of the constant is fixed, that is, the values in multiple objects are the same. If you are building a constant with a function or an object, the initialization value for its constants may be different each time you create an object. Therefore, the definition of a Java constant that uses only final is not constant.

Use the static modifier:

A storage space is created for this variable in memory before the object is created, and the storage space for this variable is shared if the static variable is needed for later creation.

If you're not sure, here's the code example (reprinted from http://advance0683.iteye.com/blog/1107732)

1 ImportJava.util.Random;2 3 //This example is to illustrate the difference between static final and final4  Public classStaticandfinaltest {5     6     Private StaticRandom Rand =NewRandom (47);//47 as a random seed, the result is a random number. 7     8     Private Final intA = Rand.nextint (20);9     Ten     Private Static Final intB = Rand.nextint (20); One  A      Public Static voidMain (string[] args) { -Staticandfinaltest SF =Newstaticandfinaltest (); -System.out.println ("SF:" + "a=" +SF.A); theSystem.out.println ("SF:" + "b=" +SF. B); -System.out.println ("------------------------------"); -Staticandfinaltest SF1 =Newstaticandfinaltest (); -System.out.println ("SF1:" + "a=" +sf1.a); +System.out.println ("SF1:" + "b=" +SF1. B); -     } +  A}

Here is the result of the code:

Sf:a=15

Sf:b=18

--------

Sf1:a=13

sf1:b=18

As you can see, in SF and SF1 objects, the value of a is not unique, but the value of B is not changed by creating a Sf1 object.

This is consistent with the above-mentioned.

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The difference between final and static final-modified constants in Java