增加 Integer 的 int 值？

Question

How do I increment a Integer's value in Java? I know I can get the value with intValue, and I can set it with new Integer(int i).

playerID.intValue()++;

does not seem to work.

Note: PlayerID is a Integer that has been created with:

Integer playerID = new Integer(1);

Answer 1

Integer objects are immutable, so you cannot modify the value once they have been created. You will need to create a new Integer and replace the existing one.

playerID = new Integer(playerID.intValue() + 1);

Answer 2

As Grodriguez says, Integer objects are immutable. The problem here is that you're trying to increment the int value of the player ID rather than the ID itself. In Java 5+, you can just write playerID++ .

As a side note, never ever call Integer 's constructor. Take advantage of autoboxing by just assigning int s to Integer s directly, like Integer foo = 5 . This will use Integer.valueOf(int) transparently, which is superior to the constructor because it doesn't always have to create a new object.

Answer 3

Java 7 and 8. Increment DOES change the reference, so it references to another Integer object. Look:

@Test
public void incInteger()
{
    Integer i = 5;
    Integer iOrig = i;
    ++i; // Same as i = i + 1;
    Assert.assertEquals(6, i.intValue());
    Assert.assertNotEquals(iOrig, i);
}

Integer by itself is still immutable.

Answer 4

AtomicInteger

Maybe this is of some worth also: there is a Java class called AtomicInteger .

This class has some useful methods like addAndGet(int delta) or incrementAndGet() (and their counterparts) which allow you to increment/decrement the value of the same instance. Though the class is designed to be used in the context of concurrency , it's also quite useful in other scenarios and probably fits your need.

final AtomicInteger count = new AtomicInteger( 0 ) ;
…
count.incrementAndGet();  // Ignoring the return value. 

Answer 5

Integer objects are immutable. You can't change the value of the integer held by the object itself, but you can just create a new Integer object to hold the result:

Integer start = new Integer(5);
Integer end = start + 5; // end == 10;

Answer 6

For Java 7, increment operator '++' works on Integers. Below is a tested example

    Integer i = new Integer( 12 );
    System.out.println(i); //12
    i = i++;
    System.out.println(i); //13

Answer 7

Maybe you can try:

final AtomicInteger i = new AtomicInteger(0);
i.set(1);
i.get();

Answer 8

You can use IntHolder as mutable alternative to Integer. But does it worth?

Answer 9

All the primitive wrapper objects are immutable.

I'm maybe late to the question but I want to add and clarify that when you do playerID++ , what really happens is something like this:

playerID = Integer.valueOf( playerID.intValue() + 1);

Integer.valueOf(int) will always cache values in the range -128 to 127, inclusive, and may cache other values outside of this range.

Answer 10

After Java 8, we can use as below

import java.lang.Math;
Math.incrementExact(playerID);
//it increment the integer value to + 1. It is also available for long