You can use the javap
tool to see for yourself. Compile the following code:
public class AutoboxingTest
{
public static void main(String []args)
{
Integer a = 3;
int b = a;
}
}
To compile and disassemble:
javac AutoboxingTest.java
javap -c AutoboxingTest
The output is:
Compiled from "AutoboxingTest.java"
public class AutoboxingTest extends java.lang.Object{
public AutoboxingTest();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return
public static void main(java.lang.String[]);
Code:
0: iconst_3
1: invokestatic #2; //Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
4: astore_1
5: aload_1
6: invokevirtual #3; //Method java/lang/Integer.intValue:()I
9: istore_2
10: return
}
Thus, as you can see, autoboxing invokes the static method Integer.valueOf()
, and autounboxing invokes intValue()
on the given Integer
object. There’s nothing else, really – it’s just syntactic sugar.