Compute a Java function's signature

Question

Is there a way to compute a Java class's method's signature? A signature
like ([Ljava/lang/String;)V represents a function that takes a String[] as argument
and returns void.

What's the rule to compute the signature?

Answer 1

It's always a set of parentheses enclosing type signifiers for the arguments, one after the other with no commas or anything, followed by a type signifier for the return value after the closing paren. It's pretty straightforward.

There's a table of type signatures on this page:

Signature    Java Type
Z    boolean
B    byte
C    char
S    short
I    int
J    long
F    float
D    double
V    void
L fully-qualified-class ;    fully-qualified-class
[ type   type[]

Those last two mean that to name a class, you say, for example, Ljava/lang/Object;, and to name an array of (for example) int, you say [I, and an array of array of int is [[I.

If you wanted to literally compute the signature in Java code based on reflection, it'd be simple enough; just use the table above with rules for handling objects and arrays.

Answer 2

Just run javap -s <class-name> in the folder containing the .class files . It will tell you with 100% accuracy. No need to guess these things.

Answer 3

A quick google search uncovered this webpage:

http://www.rgagnon.com/javadetails/java-0286.html

There are two parts to the signature. The first part is enclosed within the parentheses and represents the method's arguments. The second portion follows the closing parenthesis and represents the return type. The mapping between the Java type and C type is

Type     Chararacter 
boolean      Z 
byte         B 
char         C 
double       D 
float        F 
int          I 
long         J 
object       L 
short        S 
void         V 
array        [ 

Answer 4

See here for some details.

Basically it's params, then return value.

Answer 5

From the JLS, §8.4.2:

8.4.2 Method Signature

The signature of a method consists of the name of the method and the number and types of formal parameters to the method. A class may not declare two methods with the same signature, or a compile-time error occurs.

The example:

class Point implements Move {
  int x, y;
  abstract void move(int dx, int dy);
  void move(int dx, int dy) { x += dx; y += dy; }
}

causes a compile-time error because it declares two move methods with the same signature. This is an error even though one of the declarations is abstract.

So the "rule" is

the name of the method and the number and types of formal parameters to the method

Answer 6

You can find this information in the the Java Virtual Machine Specification