Method Class | getParameterTypes() Method in Java

Prerequisite : Java.lang.Class class in Java | Set 1, Java.lang.Class class in Java | Set 2

java.lang.reflectMethod class help us to get information of a single method on a class or interface. This class also provides access to the methods of classes and invoke them at runtime.

getParameterTypes() method of Method class:
For creating methods, many times parameters are needed for those method to work properly. The getParameterTypes() method of Method class returns an array of Class objects that represents the parameter types, declared in method at time of coding. The getParameterTypes() returns an array of length 0 if the method object takes no parameters.

Syntax:

public Class[] getParameterTypes()

Parameters: The method does not take any parameters.

Return Value: The method returns an array of Class object that represents the formal parameter types of the method object, in declaration order.

Below programs illustrate the getParameterTypes() method of Method class:

Program 1: Below program is going to print the details for array of Class objects that represent the formal parameter types of the method object defined in program.

/*
* Program Demonstrate how to apply getParameterTypes() method
* of Method Class.
*/
import java.lang.reflect.Method;
public class GFG {

    // Main method
    public static void main(String[] args)
    {
        try {
            // Create class object
            Class classobj = GFG.class;

            // Get Method Object
            Method[] methods = classobj.getMethods();

            // Iterate through methods
            for (Method method : methods) {

                // We are only taking method defined in the demo class
                // We are not taking other methods of the object class
                if (method.getName().equals("setValue")
                    || method.getName().equals("getValue")
                    || method.getName().equals("setManyValues")) {
                    // Apply getGenericParameterTypes() method
                    Class[] parameters = method.getParameterTypes();

                    // Print parameter Types of method Object
                    System.out.println("\nMethod Name : "
                                       + method.getName());
                    System.out.println("No of Parameters : "
                                       + parameters.length);
                    System.out.println("Parameter object details:");
                    for (Class classobject : parameters) {
                        System.out.println(classobject.getName());
                    }
                }
            }
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }
    // Method containing two parameter
    public void setValue(String value1, String value2)
    {
        System.out.println("setValue");
    }

    // Method containing no parameter
    public String getValue()
    {
        System.out.println("getValue");
        return "getValue";
    }

    // Method containing many parameter
    public void setManyValues(int value1, double value2, String value3)
    {
        System.out.println("setManyValues");
    }
}

Output:

Method Name : setManyValues
No of Parameters : 3
Parameter object details:
int
double
java.lang.String

Method Name : getValue
No of Parameters : 0
Parameter object details:

Method Name : setValue
No of Parameters : 2
Parameter object details:
java.lang.String
java.lang.String

Program 2: We are giving a parameter class object as input and below program going to count number of those type parameter if the Method object contains parameter otherwise program returns 0.

/*
* Program Demonstrate how to apply getParameterTypes() method
* of Method Class.
*/
import java.lang.reflect.Method;
import java.lang.reflect.Type;

public class GFG3 {

    // Main method
    public static void main(String[] args)
    {
        try {
            // Create class object
            Class classobj = sample.class;

            Method[] methods = classobj.getMethods();

            /* Check whether setManyValues() method contains
                        int parameter or not
                and print no of string parameter it contains*/

            for (Method method : methods) {
                if (method.getName().equals("setValue")) {
                    int count = containsParameter(method,
                               (Class)java.lang.String.class);
                    System.out.println("No of String "+
                        "Parameters in setValue(): " + count);
                }
            }

            /* Check whether setManyValues() method contains
                        int parameter or not
            and print no of string parameter it contains */

            for (Method method : methods) {
                if (method.getName().equals("setManyValues")) {
                    int count = containsParameter(method,
                                            (Class) int.class);
                    System.out.println("No of int Parameters"+
                             " in setManyValues(): " + count);
                }
            }
        }
        catch (Exception e) {
            e.printStackTrace();
        }
    }

    // Count no of parameters contain by method same as passed to method
    private static int containsParameter(Method method, Class parameterName)
    {
        int count = 0;

        // Get all parameter class objects  using getParameterTypes()
        Class parameters[] = method.getParameterTypes();

        for (int i = 0; i < parameters.length; i++) {
            // Check contains parameter or not
            if (parameters[i] == parameterName) {
                count++;
            }
        }

        return count;
    }
}
// A simple class
class sample {

    // Method containing two parameter
    public void setValue(String value1, String value2)
    {
        System.out.println("setValue");
    }

    // Method containing many parameter
    public void setManyValues(int value1, double value2, String value3)
    {
        System.out.println("setManyValues");
    }
}

Output:

No of String Parameters in setValue(): 2
No of int Parameters in setManyValues(): 1

Reference:
Oracle Doc for getParameterTypes()