Implement Halstead for Java (#811)

Author: dburriss

src/getter.rs

@@ -524,4 +524,43 @@ impl Getter for JavaCode {
             _ => SpaceKind::Unknown,
         }
     }
+
+    fn get_op_type(node: &Node) -> HalsteadType {
+        use Java::*;
+        // Some guides that informed grammar choice for Halstead
+        // keywords, operators, literals: https://docs.oracle.com/javase/specs/jls/se18/html/jls-3.html#jls-3.12
+        // https://www.geeksforgeeks.org/software-engineering-halsteads-software-metrics/?msclkid=5e181114abef11ecbb03527e95a34828
+        let typ = node.object().kind_id();
+
+        match typ.into() {
+            // Operator: function calls
+            MethodInvocation
+            // Operator: control flow
+            | If | Else | Switch | Case | Try | Catch | Throw | Throws | Throws2 | For | While | Continue | Break | Do | Finally
+            // Operator: keywords
+            | New | Return | Default | Abstract | Assert | Instanceof | Extends | Final | Implements | Transient | Synchronized | Super | This | VoidType
+            // Operator: brackets and comma and terminators (separators)
+            | SEMI | COMMA | COLONCOLON | LBRACE | LBRACK | LPAREN | RBRACE | RBRACK | RPAREN | DOTDOTDOT | DOT
+            // Operator: operators
+            | EQ | LT | GT | BANG | TILDE | QMARK | COLON // no grammar for lambda operator ->
+            | EQEQ | LTEQ | GTEQ | BANGEQ | AMPAMP | PIPEPIPE | PLUSPLUS | DASHDASH
+            | PLUS | DASH | STAR | SLASH | AMP | PIPE | CARET | PERCENT| LTLT | GTGT | GTGTGT
+            | PLUSEQ | DASHEQ | STAREQ | SLASHEQ | AMPEQ | PIPEEQ | CARETEQ | PERCENTEQ | LTLTEQ | GTGTEQ | GTGTGTEQ
+            // type identifier
+            | TypeIdentifier | IntegralType | FloatingPointType | BooleanType
+            => {
+                HalsteadType::Operator
+            },
+            // Operands: variables, constants, literals
+            Identifier | NullLiteral | ClassLiteral | StringLiteral | CharacterLiteral | HexIntegerLiteral | OctalIntegerLiteral
+            | BinaryIntegerLiteral | DecimalIntegerLiteral | HexFloatingPointLiteral | DecimalFloatingPointLiteral  => {
+                HalsteadType::Operand
+            },
+            _ => {
+                HalsteadType::Unknown
+            },
+        }
+    }
+
+    get_operator!(Java);
 }

src/metrics/halstead.rs

@@ -325,9 +325,14 @@ impl Halstead for CppCode {
     }
 }
 
+impl Halstead for JavaCode {
+    fn compute<'a>(node: &Node<'a>, code: &'a [u8], halstead_maps: &mut HalsteadMaps<'a>) {
+        compute_halstead::<Self>(node, code, halstead_maps);
+    }
+}
+
 impl Halstead for PreprocCode {}
 impl Halstead for CcommentCode {}
-impl Halstead for JavaCode {}
 
 #[cfg(test)]
 mod tests {
@@ -521,4 +526,27 @@ mod tests {
             ]
         );
     }
+
+    #[test]
+    fn java_operators_and_operands() {
+        check_metrics!(
+            "public class Main {
+            public static void main(String args[]) {
+                  int a, b, c, avg;
+                  a = 5; b = 5; c = 5;
+                  avg = (a + b + c) / 3;
+                  MessageFormat.format(\"{0}\", avg);
+                }
+            }",
+            "foo.java",
+            JavaParser,
+            halstead,
+            [
+                (u_operators, 16, usize), // { void ; ( String [ ] ) , int = + / format . }
+                (operators, 34, usize),
+                (u_operands, 12, usize), // Main main args a b c avg 5 3 MessageFormat format "{0}"
+                (operands, 22, usize)
+            ]
+        );
+    }
 }