How do I invoke a method using Method class?

By Wayan in Reflection 0 Comment

This example demonstrate using reflection to invoke methods of a class object. Using reflection we can call method of an object using the given string name of the method. When using this method we need to catch for the NoSuchMethodException, IllegalAccessException and InvocationTargetException.

package org.kodejava.lang.reflect;

import java.lang.reflect.Method;
import java.lang.reflect.InvocationTargetException;

public class InvokingMethod {
    public static void main(String[] args) {
        InvokingMethod object = new InvokingMethod();
        Class<? extends InvokingMethod> clazz = object.getClass();

        try {
            // Invoking the add(int, int) method
            Method method = clazz.getMethod("add", int.class, int.class);
            Object result = method.invoke(object, 10, 10);
            System.out.println("Result = " + result);

            // Invoking the multiply(int, int) method
            method = clazz.getMethod("multiply", int.class, int.class);
            result = method.invoke(object, 10, 10);
            System.out.println("Result = " + result);

        } catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {
            e.printStackTrace();
        }
    }

    public int add(int numberA, int numberB) {
        return numberA + numberB;
    }

    public int multiply(int numberA, int numberB) {
        return numberA * numberB;
    }
}

How do I get the methods of a class object?

By Wayan in Reflection 0 Comment

In this example we show you how to get the methods available in a class object. We show three ways to get the methods, they are:

  • Class.getDeclaredMethods()
  • Class.getMethods()
  • Class.getMethod(String, Class<?>...)
package org.kodejava.lang.reflect;

import java.lang.reflect.Method;

public class GetMethods {
    public static void main(String[] args) {
        GetMethods object = new GetMethods();
        Class<? extends GetMethods> clazz = object.getClass();

        // Get all declared methods including public, protected, private and
        // package (default) access but excluding the inherited methods.
        Method[] methods = clazz.getDeclaredMethods();
        for (Method method : methods) {
            System.out.println("Method name        = " + method.getName());
            System.out.println("Method return type = " + method.getReturnType().getName());

            Class<?>[] paramTypes = method.getParameterTypes();
            for (Class<?> c : paramTypes) {
                System.out.println("Param type         = " + c.getName());
            }

            System.out.println("----------------------------------------");
        }

        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");

        // Get all methods including the inherited method. Using the getMethods()
        // we can only access public methods.
        methods = clazz.getMethods();
        for (Method method : methods) {
            System.out.println("Method name        = " + method.getName());
            System.out.println("Method return type = " + method.getReturnType().getName());

            Class<?>[] paramTypes = method.getParameterTypes();
            for (Class<?> c : paramTypes) {
                System.out.println("Param type         = " + c.getName());
            }

            System.out.println("----------------------------------------");
        }

        try {
            // We can also get method by their name and parameter types, here we
            // are trying to get the add(int, int) method.
            Method method = clazz.getMethod("add", int.class, int.class);
            System.out.println("Method name: " + method.getName());
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }
    }

    public int add(int numberA, int numberB) {
        return numberA + numberB;
    }

    protected int multiply(int numberA, int numberB) {
        return numberA * numberB;
    }

    private double div(int numberA, int numberB) {
        return numberA / numberB;
    }
}

How do I get the path from where a class is loaded?

By Wayan in Core API, Lang Package 0 Comment

This examples shows how to get a path name or location from where our class is loaded.

package org.kodejava.lang;

public class CodeSourceLocation {
    public static void main(String[] args) {
        CodeSourceLocation csl = new CodeSourceLocation();
        csl.getCodeSourceLocation();
    }

    private void getCodeSourceLocation() {
        // The location from where the class is loaded.
        System.out.println("Code source location: " +
            getClass().getProtectionDomain().getCodeSource().getLocation());
    }
}

The code snippet print the following output:

Code source location: file:/F:/Wayan/Kodejava/kodejava-example/kodejava-lang/target/classes/

How do I get the name of a class?

By Wayan in Core API, Lang Package 0 Comment 
package org.kodejava.lang;

import java.util.Calendar;
import java.math.BigDecimal;

public class ClassName {
    public static void main(String[] args) {
        // Get the name of the classes below.
        Class<?> clazz = String.class;
        System.out.println("Class Name: " + clazz.getName());

        clazz = Calendar.class;
        System.out.println("Class Name: " + clazz.getName());

        clazz = BigDecimal.class;
        System.out.println("Class Name: " + clazz.getName());
    }
}

The result of the code snippet above are:

Class Name: java.lang.String
Class Name: java.util.Calendar
Class Name: java.math.BigDecimal

How do I know if a class object is an interface or a class?

By Wayan in Core API, Lang Package 0 Comment 
package org.kodejava.lang;

public class CheckForInterface {
    public static void main(String[] args) {
        // Checking whether Cloneable is an interface or class
        Class<?> clazz = Cloneable.class;
        boolean isInterface = clazz.isInterface();
        System.out.println(clazz.getName() + " is an interface = " + isInterface);

        // Checking whether String is an interface or class
        clazz = String.class;
        isInterface = clazz.isInterface();
        System.out.println(clazz.getName() + " is an interface = " + isInterface);
    }
}

java.lang.Cloneable is an interface = true
java.lang.String is an interface = false