In this post, we will see how to invoke the method using reflection in java.
Table of Contents
Create a class named
Employee.java. We will invoke this class’s method using reflection.
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package org.arpit.java2blog.methodinvocation; public class Employee { String name; int age; String address; public Employee(String name, int age, String address) { super(); this.name = name; this.age = age; this.address = address; } public void printName(String name) { System.out.println("Name:"+ name); } protected void printAge(int age) { System.out.println("Age : "+age); } private void printAddress(String address) { System.out.println("Address : "+address); } public String toString() { return name+"_"+age+"_"+address; } public static void printNationality() { System.out.println("Nationality: Indian"); } } |
Create a main method named EmployeeReflectionMain.java.
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package org.arpit.java2blog.methodinvocation; import java.lang.reflect.Constructor; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; public class EmployeeReflectionMain { public static void main(String[] args) { Class<Employee> cls; // For constructor invocation Class[] constructorEmp = new Class[] { String.class, int.class ,String.class}; String name="John"; int age=20; String address="HighStreet"; Constructor empConst; Object[] constArgs = new Object[] { name,age,address}; try { cls = (Class<Employee>) Class.forName("org.arpit.java2blog.methodinvocation.Employee"); empConst = cls.getConstructor(constructorEmp); Employee e = (Employee) empConst.newInstance(constArgs); System.out.println("================================"); System.out.println("Calling printName method using reflection"); System.out.println("================================"); //String parameter Class[] paramString = new Class[1]; paramString[0] = String.class; //call the printName method and need to pass string parameter Method method = cls.getMethod("printName", paramString); method.invoke(e, e.name); System.out.println("================================"); System.out.println("Calling protected printAge method using reflection"); System.out.println("================================"); //int parameter Class[] paramInt = new Class[1]; paramInt[0] = Integer.TYPE; //call the printAge method and need to pass Integer parameter // As printAge is protected, need to call cls.getDeclaredMethod method = cls.getDeclaredMethod("printAge", paramInt); method.invoke(e, e.age); System.out.println("================================"); System.out.println("Calling toString method using reflection and capturing return value"); System.out.println("================================"); //no paramater Class noparams[] = {}; method = cls.getDeclaredMethod("toString", noparams); String toStringStr=(String) method.invoke(e, null); System.out.println(toStringStr); System.out.println("================================"); System.out.println("Calling static method printNationality using Reflection"); System.out.println("================================"); method = cls.getMethod("printNationality", noparams); method.invoke(null,null); System.out.println("================================"); System.out.println("Calling private method printAddress using Reflection"); System.out.println("================================"); method = cls.getDeclaredMethod("printAddress", paramString); method.setAccessible(true); method.invoke(e,e.address); } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | NoSuchMethodException | SecurityException | IllegalArgumentException | InvocationTargetException e) { e.printStackTrace(); } } } |
When you run above program, you will get below output:
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Calling printName method using reflection
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Name:John
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Calling protected printAge method using reflection
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Age : 20
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Calling toString method using reflection and capturing return value
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John_20_HighStreet
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Calling static method printNationality using Reflection
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Nationality: Indian
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Calling private method printAddress using Reflection
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Address : HighStreet
Calling printName method using reflection
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Name:John
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Calling protected printAge method using reflection
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Age : 20
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Calling toString method using reflection and capturing return value
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John_20_HighStreet
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Calling static method printNationality using Reflection
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Nationality: Indian
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Calling private method printAddress using Reflection
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Address : HighStreet
Explanation
You need to first create an object of Class.We will get all the info such as constructors, methods and fields using this cls object.
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Class cls = (Class) Class.forName("org.arpit.java2blog.methodinvocation.Employee"); |
Invoke method without parameters
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//no parameter Class noparams[] = {}; method = cls.getDeclaredMethod("toString", noparams); String toStringStr=(String) method.invoke(e, null); System.out.println(toStringStr); |
You need to use getDeclareMethod() to get toString() method and toString() do not have any parameter hence, we will pass empty params.
Invoke method with parameters
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//String parameter Class[] paramString = new Class[1]; paramString[0] = String.class; //call the printName method and need to pass string parameter Method method = cls.getMethod("printName", paramString); method.invoke(e, e.name); |
As printName() is public method, we can use getMethod() to get method of the object and pass String parameter to printName() method.
Invoke static method using reflection
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//no parameter Class noparams[] = {}; method = cls.getMethod("printNationality", noparams); method.invoke(null,null); |
As you can see, we don’t require any object for static method, we are invoking methods using method.invoke(null,null).
Invoke private method using reflection
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//String parameter Class[] paramString = new Class[1]; paramString[0] = String.class; method = cls.getDeclaredMethod("printAddress", paramString); method.setAccessible(true); method.invoke(e,e.address); |
If you want to invoke private method using reflection, you need call method.setAccessible(true) explicitly and then only you can access private method.
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