How to check whether a method exists in a Java class or not?

Using Class.getMethod(), we can check whether a method with given name exists or not.

 

public Method getMethod(String name, Class<?>... parameterTypes) throws NoSuchMethodException, SecurityException

Return a Method object, if the method with given name and respective parameters exists, else it throws NoSuchMethodException.

 

Below snippet return true, if the method name exists with respective arguments, else false.

public static boolean isMethodExist(Class clazz, String methodName, Class<?>... parameterTypes) {

	try {
		clazz.getMethod(methodName, parameterTypes);
	} catch (NoSuchMethodException e) {
		return false;
	}
	return true;
}

 

If you are not sure about the method arguments and interested only in method name, you can use getDeclaredMethods method. Class.getDeclaredMethods return all the methods declared in this class.

 

Below snippet return true, if the method with given name exists, else false.

public static boolean isMethodExist(Class clazz, String methodName) {
	try {

		Method[] declaredMethods = clazz.getDeclaredMethods();

		for (Method method : declaredMethods) {
			if (method.getName().equals(methodName)) {
				return true;
			}
		}

	} catch (Exception e) {
		e.printStackTrace();
	}

	return false;
}

Find the below working application.

 

ArithmeticUtil.java

package com.sample.app.util;

public class ArithmeticUtil {

	public int add(int a, int b) {
		return a + b;
	}

	public int add(int a, int b, int c) {
		return a + b + c;
	}

	public int sub(int a, int b) {
		return a - b;
	}

}

ReflectionUtil.java

package com.sample.app.util;

import java.lang.reflect.Method;

public class ReflectionUtil {

	public static boolean isMethodExist(Class clazz, String methodName, Class<?>... parameterTypes) {

		try {
			clazz.getMethod(methodName, parameterTypes);
		} catch (NoSuchMethodException e) {
			return false;
		}
		return true;
	}

	public static boolean isMethodExist(Class clazz, String methodName) {
		try {

			Method[] declaredMethods = clazz.getDeclaredMethods();

			for (Method method : declaredMethods) {
				if (method.getName().equals(methodName)) {
					return true;
				}
			}

		} catch (Exception e) {
			e.printStackTrace();
		}

		return false;
	}

}

App.java

package com.sample.app;

import com.sample.app.util.ArithmeticUtil;
import com.sample.app.util.ReflectionUtil;

public class App {
	public static void main(String[] args) {
		boolean exists = ReflectionUtil.isMethodExist(ArithmeticUtil.class, "add", int.class, int.class);
		System.out.println("Is add method with two integer arguments exists : " + exists);

		exists = ReflectionUtil.isMethodExist(ArithmeticUtil.class, "sub", int.class, int.class);
		System.out.println("Is sub method with two integer arguments exists : " + exists);

		exists = ReflectionUtil.isMethodExist(ArithmeticUtil.class, "mul", int.class, int.class);
		System.out.println("Is mul method with two integer arguments exists : " + exists);

		exists = ReflectionUtil.isMethodExist(ArithmeticUtil.class, "add");
		System.out.println("\nIs add method exists : " + exists);

		exists = ReflectionUtil.isMethodExist(ArithmeticUtil.class, "sub");
		System.out.println("Is sub method exists : " + exists);

		exists = ReflectionUtil.isMethodExist(ArithmeticUtil.class, "mul");
		System.out.println("Is mul method exists : " + exists);
	}
}

Output

Is add method with two integer arguments exists : true
Is sub method with two integer arguments exists : true
Is mul method with two integer arguments exists : false

Is add method exists : true
Is sub method exists : true
Is mul method exists : false

 

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