Java reflection get class implements interface

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In Java, every type is either a reference or a primitive. Classes, enums, and arrays (which all inherit from java.lang.Object), as well as interfaces, are all reference types. Examples of reference types include java.lang.String, all of the wrapper classes for primitive types such as java.lang.Double, the interface java.io.Serializable, and the enum javax.swing.SortOrder. There is a fixed set of primitive types: boolean, byte, short, int, long, char, float, and double.

java.lang.Class is the entry point for all the reflection operations. For every type of object, JVM instantiates an immutable instance of java.lang.Class that provides methods to examine the runtime properties of the object and create new objects, invoke its method and get/set object fields.

The source code for this post is available on GitHub.

The below class diagram shows a list of Reflection APIs offered by java.lang.Class.

Java Reflection for Classes

2. Reflection Class API Examples

• Get Class Object
• Get Super Class
• Get Public Member Classes
• Get Declared Classes
• Get Declaring Class
• Getting Package Name
• Getting Class Modifiers
• Get Type Parameters
• Get Implemented Interfaces
• Get All Public Methods
• Get All Public Constructors
• Get All Public Fields
• Get All Annotations

In this article, we will look into all the above important methods of Class. Let’s first create BaseInterface, BaseClass and ConcreteClass then we will apply all the reflection API’s on these reference types.

BaseInterface.java

package com.javaguides.reflection.classes; /** * Base Interface * @author javaguides.net * */ public interface BaseInterface < void method1(); void method2(String str); void method3(int a); >

BaseClass.java

package com.javaguides.reflection.classes; /** * * @author javaguides.net * */ public class BaseClass < public void method4()< System.out.println("method4"); > public void method5()< System.out.println("method5"); > public void method6()< System.out.println("method6"); > >

ConcreteClass.java

package com.javaguides.reflection.classes; /** * Concrete class * @author javaguides.net * */ @Deprecated public class ConcreteClass extends BaseClass implements BaseInterface < public int id; private String name; public ConcreteClass(int id)< this.id = id; > public void method1() < System.out.println("ConcreteClass :: method 1"); > public void method2(String str) < System.out.println("ConcreteClass :: method 2"); > public void method3(int a) < System.out.println("ConcreteClass :: method 3"); > // Inner classes private class InnerPrivateClass < >public class InnerPublicClass < >protected class InnerProtectedClass < >class InnerDefaultClass < >// Member enum public enum ConcreClassMemberEnum < >// Member Interface public interface ConcreteMemberInterface < >>

2.1 Get Class Object

• forName() method of Class class
• getClass() method of Object class
• the .class syntax

ClassBaseClass> baseClass = BaseClass.class; System.out.println(baseClass.getCanonicalName()); // using forName() method // Returns the Class object associated with the class or interface with // the given string name Class concreteClass = Class.forName("com.javaguides.reflection.classes.ConcreteClass"); System.out.println(concreteClass.getSimpleName()); // for primitive types Class booleanClass = boolean.class; System.out.println(booleanClass.getCanonicalName()); // prints boolean // wrapper classes Class cDouble = Double.TYPE; System.out.println(cDouble.getCanonicalName()); // prints double // For arrays Class cDoubleArray = Class.forName("[D"); System.out.println(cDoubleArray.getCanonicalName()); // prints double[] // Two Dimensional array. Class twoDStringArray = String[][].class; System.out.println(twoDStringArray.getCanonicalName()); // prints //  java.lang.String[][] // For Collections SetString> s = new HashSetString>(); Class c4 = s.getClass(); System.out.println(c4.getCanonicalName()); // For String Class c = "foo".getClass(); System.out.println(c.getCanonicalName());

com.javaguides.reflection.classes.BaseClass ConcreteClass boolean double double[] java.lang.String[][] java.util.HashSet java.lang.String 

2.2 Get Super Class

getSuperclass() method on a Class object returns the superclass of the class. If this Class represents either the Object class, an interface, a primitive type, or void, then null is returned. If this object represents an array class then the Class object representing the Object class is returned.

// Get super class BaseClass of ConcreteClass. Class concreteClass = Class.forName("com.javaguides.reflection.classes.ConcreteClass"); System.out.println(concreteClass.getSuperclass()); // Get super class of Object class System.out.println(Object.class.getSuperclass()); // prints null // Get super class of String class System.out.println(String.class.getSuperclass()); // Get super class of String[] System.out.println(String[].class.getSuperclass()); // Get Super class of Integer class System.out.println(Integer.class.getSuperclass());

class com.javaguides.reflection.classes.BaseClass null class java.lang.Object class java.lang.Object class java.lang.Number 

2.3 Get Public Member Classes

getClasses() method of a Class representation of object returns an array containing Class objects representing all the public classes, interfaces and enums that are members of the class represented by this Class object. This includes public class and interface members inherited from superclasses and public class and interface members declared by the class. This method returns an array of length 0 if this Class object has no public member classes or interfaces or if this Class object represents a primitive type, an array class, or void.

Class concreteClass = Class.forName("com.javaguides.reflection.classes.ConcreteClass"); Class [] classes = concreteClass.getClasses(); for (Class class1 : classes) < System.out.println(class1.getCanonicalName()); >

com.javaguides.reflection.classes.ConcreteClass.ConcreClassMemberEnum com.javaguides.reflection.classes.ConcreteClass.ConcreteMemberInterface com.javaguides.reflection.classes.ConcreteClass.InnerPublicClass 

2.4 Get Declared Classes

getDeclaredClasses() method returns an array of Class objects reflecting all the classes and interfaces declared as members of the class represented by this Class object. The returned array doesn’t include classes declared in inherited classes and interfaces.

Class concreteClass = Class.forName("com.javaguides.reflection.classes.ConcreteClass"); Class [] classes = concreteClass.getDeclaredClasses(); for (Class class1 : classes) < System.out.println(class1.getCanonicalName()); >

com.javaguides.reflection.classes.ConcreteClass.ConcreClassMemberEnum com.javaguides.reflection.classes.ConcreteClass.ConcreteMemberInterface com.javaguides.reflection.classes.ConcreteClass.InnerDefaultClass com.javaguides.reflection.classes.ConcreteClass.InnerPrivateClass com.javaguides.reflection.classes.ConcreteClass.InnerProtectedClass com.javaguides.reflection.classes.ConcreteClass.InnerPublicClass 

2.6 Get Declaring Class

getDeclaringClass() method returns the Class object representing the class in which it was declared.

Class concreteClass = Class.forName("com.javaguides.reflection.classes.ConcreteClass$InnerProtectedClass"); System.out.println(concreteClass.getDeclaringClass().getCanonicalName()); // prints com.javaguides.reflection.classes.ConcreteClass

com.javaguides.reflection.classes.ConcreteClass 

2.7 Getting Package Name

getPackage() method returns the package for this class. The class loader of this class is used to find the package. We can invoke getName() method of Package to get the name of the package.

Class concreteClass = Class.forName("com.javaguides.reflection.classes.ConcreteClass"); System.out.println(concreteClass.getPackage());

package com.javaguides.reflection.classes 

2.8 Getting Class Modifiers

getModifiers() method returns the int representation of the class modifiers, we can use java.lang.reflect.Modifier.toString() method to get it in the string format as used in source code.

Class concreteClass = Class.forName("com.javaguides.reflection.classes.ConcreteClass"); System.out.println(Modifier.toString(concreteClass.getModifiers())); // prints public

2.9 Get Type Parameters

getTypeParameters() returns the array of TypeVariable if there are any Type parameters associated with the class. The type parameters are returned in the same order as declared.

//Get Type parameters (generics) TypeVariable [] typeParameters = Class.forName("java.util.HashMap").getTypeParameters(); for(TypeVariable t : typeParameters) System.out.print(t.getName()+",");

2.10 Get Implemented Interfaces

getGenericInterfaces() method returns the array of interfaces implemented by the class with generic type information. We can also use getInterfaces() to get the class representation of all the implemented interfaces.

Type[] interfaces = Class.forName("java.util.HashMap").getGenericInterfaces(); // prints "[java.util.Map, interface java.lang.Cloneable, // interface java.io.Serializable]" System.out.println(Arrays.toString(interfaces)); // prints "[interface java.util.Map, interface java.lang.Cloneable, // interface java.io.Serializable]" System.out.println(Arrays.toString(Class.forName("java.util.HashMap").getInterfaces()));

[java.util.Map, interface java.lang.Cloneable, interface java.io.Serializable] [interface java.util.Map, interface java.lang.Cloneable, interface java.io.Serializable] 

2.11 Get All Public Methods

getMethods() method returns the array of public methods of the Class including public methods of it’s superclasses and super interfaces.

Class concreteClass = Class.forName("com.javaguides.reflection.classes.ConcreteClass"); Method[] methods = concreteClass.getMethods(); for (Method method : methods) < System.out.println(method.getName()); >

method1 method2 method3 method4 method5 method6 wait wait wait equals toString hashCode getClass notify notifyAll 

2.12 Get All Public Constructors

getConstructors() method returns the list of public constructors of the class reference of the object.

Class concreteClass = Class.forName("com.javaguides.reflection.classes.ConcreteClass"); Constructor [] constructors = concreteClass.getConstructors(); for (Constructor constructor : constructors) < System.out.println(constructor.getName()); >

com.javaguides.reflection.classes.ConcreteClass 

2.13 Get All Public Fields

getFields() method returns the array of public fields of the class including public fields of its superclasses and super interfaces.

Class concreteClass = Class.forName("com.javaguides.reflection.classes.ConcreteClass"); Field[] fields = concreteClass.getFields(); for (Field field : fields) < System.out.println(field.getName()); >

2.14 Get All Annotations

getAnnotations() method returns all the annotations for the element, we can use it with class, fields, and methods also.

Class concreteClass = Class.forName("com.javaguides.reflection.classes.ConcreteClass"); Annotation[] annotations = concreteClass.getAnnotations(); for (Annotation annotation : annotations) < System.out.println(annotation); >

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