public static Double functionCalling()

in java/src/main/java/com/example/gemini/FunctionCalling.java [36:142]
91 lines of code
4 McCabe index (conditional complexity)

    public static Double functionCalling() {
        // [START function_calling]
        Client client = new Client();

        FunctionDeclaration addFunction =
                FunctionDeclaration.builder()
                        .name("addNumbers")
                        .parameters(
                                Schema.builder()
                                        .type("object")
                                        .properties(Map.of(
                                                "firstParam", Schema.builder().type("number").description("First number").build(),
                                                "secondParam", Schema.builder().type("number").description("Second number").build()))
                                        .required(Arrays.asList("firstParam", "secondParam"))
                                        .build())
                        .build();

        FunctionDeclaration subtractFunction =
                FunctionDeclaration.builder()
                        .name("subtractNumbers")
                        .parameters(
                                Schema.builder()
                                        .type("object")
                                        .properties(Map.of(
                                                "firstParam", Schema.builder().type("number").description("First number").build(),
                                                "secondParam", Schema.builder().type("number").description("Second number").build()))
                                        .required(Arrays.asList("firstParam", "secondParam"))
                                        .build())
                        .build();

        FunctionDeclaration multiplyFunction =
                FunctionDeclaration.builder()
                        .name("multiplyNumbers")
                        .parameters(
                                Schema.builder()
                                        .type("object")
                                        .properties(Map.of(
                                                "firstParam", Schema.builder().type("number").description("First number").build(),
                                                "secondParam", Schema.builder().type("number").description("Second number").build()))
                                        .required(Arrays.asList("firstParam", "secondParam"))
                                        .build())
                        .build();

        FunctionDeclaration divideFunction =
                FunctionDeclaration.builder()
                        .name("divideNumbers")
                        .parameters(
                                Schema.builder()
                                        .type("object")
                                        .properties(Map.of(
                                                "firstParam", Schema.builder().type("number").description("First number").build(),
                                                "secondParam", Schema.builder().type("number").description("Second number").build()))
                                        .required(Arrays.asList("firstParam", "secondParam"))
                                        .build())
                        .build();

        GenerateContentConfig config = GenerateContentConfig.builder()
                .toolConfig(ToolConfig.builder().functionCallingConfig(
                        FunctionCallingConfig.builder().mode("ANY").build()
                ).build())
                .tools(
                        Collections.singletonList(
                                Tool.builder().functionDeclarations(
                                        Arrays.asList(
                                                addFunction,
                                                subtractFunction,
                                                divideFunction,
                                                multiplyFunction
                                        )
                                ).build()

                        )
                )
                .build();

        GenerateContentResponse response =
                client.models.generateContent(
                        "gemini-2.0-flash",
                        "I have 57 cats, each owns 44 mittens, how many mittens is that in total?",
                        config);


        if (response.functionCalls() == null || response.functionCalls().isEmpty()) {
            System.err.println("No function call received");
            return null;
        }

        var functionCall = response.functionCalls().getFirst();
        String functionName = functionCall.name().get();
        var arguments = functionCall.args();

        Map<String, BiFunction<Double, Double, Double>> functionMapping = new HashMap<>();
        functionMapping.put("addNumbers", (a, b) -> a + b);
        functionMapping.put("subtractNumbers", (a, b) -> a - b);
        functionMapping.put("multiplyNumbers", (a, b) -> a * b);
        functionMapping.put("divideNumbers", (a, b) -> b != 0 ? a / b : Double.NaN);

        BiFunction<Double, Double, Double> function = functionMapping.get(functionName);

        Number firstParam = (Number) arguments.get().get("firstParam");
        Number secondParam = (Number) arguments.get().get("secondParam");
        Double result = function.apply(firstParam.doubleValue(), secondParam.doubleValue());

        System.out.println(result);
        // [END function_calling]
        return result;
    }