Java.lang.Class class in Java | Set 2

Difficulty Level : Basic
Last Updated : 03 Apr, 2017

Java.lang.Class class in Java | Set 1
More methods:

int getModifiers() : This method returns the Java language modifiers for this class or interface, encoded in an integer. The modifiers consist of the Java Virtual Machine’s constants for public, protected, private, final, static, abstract and interface. These modifiers are already decoded in Modifier class in java.lang.Reflect package.

Syntax : 
public int getModifiers()
Parameters : 
NA
Returns :
the int representing the modifiers for this class

// Java program to demonstrate getModifiers() method
  
import java.lang.reflect.Modifier;
  
public abstract class Test
{
    public static void main(String[] args) 
    {
        // returns the Class object associated with Test class
        Class c = Test.class;
  
        // returns the Modifiers of the class Test
        // getModifiers method
        int i = c.getModifiers();
          
        System.out.println(i);
          
        System.out.print("Modifiers of " + c.getName() + " class are : ");
  
        // getting decoded i using toString() method
        // of Modifier class
        System.out.println(Modifier.toString(i));
    }
}

Output:

1025
Modifiers of Test class are : public abstract

T[] getEnumConstants() : This method returns the elements of this enum class. It returns null if this Class object does not represent an enum type.

Syntax : 
public T[] getEnumConstants()
Parameters : 
NA
Returns :
an array containing the values comprising the enum class represented by this Class object
in the order they're declared,
or null if this Class object does not represent an enum type

// Java program to demonstrate getEnumConstants() method
  
enum Color
{
    RED, GREEN, BLUE;
}
   
public class Test
{
    public static void main(String[] args) 
    {   
        // returns the Class object associated with Color(an enum class)
        Class c1 = Color.class;
          
        // returns the Class object associated with Test class
        Class c2 = Test.class;
          
        // returns the elements of Color enum class in an array
        // getEnumConstants method
        Object[] obj1 = c1.getEnumConstants();
          
        System.out.println("Enum constants of " + c1.getName() + " class are :");
          
        // iterating through enum constants
        for (Object object : obj1)
        {
            System.out.println(object);
        }
          
        // returns null as Test Class object does not represent an enum type
        Object[] obj2 = c2.getEnumConstants();
  
        System.out.println("Test class does not contain any Enum constant.");
        System.out.println(obj2);
          
    }
}

Output:

Enum constants of Color class are :
RED
GREEN
BLUE
Test class does not contain any Enum constant.
null

String getCanonicalName() : This method returns the canonical name of the underlying class as defined by the Java Language Specification.
It returns null if the underlying class does not have a canonical name (i.e., if it is a local or anonymous class or an array whose component type does not have a canonical name).

Syntax : 
public String getCanonicalName()
Parameters : 
NA
Returns :
the Canonical name of the underlying class, if it exists
null, otherwise

// Java program to demonstrate getCanonicalName() method
public class Test
{
    public static void main(String[] args) 
            throws ClassNotFoundException 
    {
        // returns the Class object for the class 
        // with the specified name 
        Class c1 = Class.forName("java.lang.String");
  
        System.out.print("Canonical name of class represented by c1 : ");
          
        // returns the Canonical name of the class
        // getCanonicalName method
        System.out.println(c1.getCanonicalName());
    }
}

Output:

Canonical name of class represented by c1 : java.lang.String

boolean desiredAssertionStatus() : This method returns the assertion status that would be assigned to this class if it were to be initialized at the time this method is invoked.

Syntax : 
public boolean desiredAssertionStatus()
Parameters : 
NA
Returns :
the desired assertion status of the specified class.

// Java program to demonstrate desiredAssertionStatus() method
public class Test
{
    public static void main(String[] args)
                         throws ClassNotFoundException
    {
        // returns the Class object for the class 
        // with the specified name 
        Class c1 = Class.forName("java.lang.String");
          
        // checking for assertion status of String class
          
        System.out.print("desired assertion status of " + c1.getName() + "class: ");
          
        // desiredAssertionStatus() method
        System.out.println(c1.desiredAssertionStatus());
          
    }
}

Output:

desired assertion status of java.lang.Stringclass : false

Class<?> getComponentType() : This method returns the Class representing the component type of an array. If this class does not represent an array class this method returns null.

Syntax : 
public Class<?> getComponentType()
Parameters : 
NA
Returns :
the Class representing the component type of this class if this class is an array

// Java program to demonstrate getComponentType() method
public class Test
{
    public static void main(String[] args)
    {
        int a[] = new int[2];
          
        // returns the Class object for array class
        Class c = a.getClass();
          
        System.out.print("Component type of class represented by c : ");
          
        // getComponentType() method
        System.out.println(c.getComponentType());
          
    }
}

Output:

Component type of class represented by c : int

Class<?>[] getDeclaredClasses() : Returns an array of Class objects reflecting all the classes and interfaces declared as members of the class represented by this Class object.
This method includes public, protected, default (package) access, and private classes and interfaces declared by the class, but excludes inherited classes and interfaces. This method returns an array of length 0 if the class declares no classes or interfaces as members, or if this Class object represents a primitive type, an array class, or void.

Syntax : 
public Class<?>[] getDeclaredClasses()
Parameters : 
NA
Returns :
the array of Class objects representing all the declared members of this class
Throws :
SecurityException - If a security manager, s, is present

// Java program to demonstrate getDeclaredClasses() method
  
public class Test
{
    // base interface
    interface A
    {
        // methods and constant declarations
    }
       
    // derived class
    class B implements A
    {
        // methods implementations that were declared in A
    }
  
      
    public static void main(String[] args)
    {
        // returns the Class object associated with Test class
        Class myClass = Test.class;
          
        // getDeclaredClasses on myClass
        // it returns array of classes and interface declare in Test class
        Class c[] = myClass.getDeclaredClasses();
          
        System.out.println("Declared classes and interfaces present in " + 
                                                  myClass.getName() + " class : ");
          
        // iterating through classes and interfaces declared in Test class
        for (Class class1 : c)
        {
            System.out.println(class1);
        }
          
    }
}

Output:

Declared classes and interfaces present in Test class : 
interface Test$A
class Test$B

Field getDeclaredField(String fieldName) : This method returns a Field object that reflects the specified declared field of the class or interface represented by this Class object.
The name parameter is a String that specifies the simple name of the desired field. Note that this method will not reflect the length field of an array class.

Syntax : 
public Field getDeclaredField(String fieldName) 
throws NoSuchFieldException,SecurityException
Parameters : 
fieldName -  the field name
Returns :
the Field object for the specified field in this class
Throws :
NoSuchFieldException - if a field with the specified name is not found.
NullPointerException - if fieldName is null
SecurityException - If a security manager, s, is present.

// Java program to demonstrate getDeclaredField() method
  
import java.lang.reflect.Field;
  
public class Test
{
    // any declared field
    int i;
      
    public static void main(String[] args) 
            throws NoSuchFieldException, SecurityException
    {
        // returns the Class object associated with Test class
        Class myClass = Test.class;
          
        // getDeclaredField on myClass
        Field f = myClass.getDeclaredField("i");
          
        System.out.println("Declared field present in " +
                                     myClass.getName() + 
                                     " class specified by \"i\" : ");
          
        System.out.println(f);
    }
}

Output:

Declared field present in Test class specified by "i" : 
int Test.i

Field[] getDeclaredFields() : This method returns an array of Field objects reflecting all the fields declared by the class or interface represented by this Class object. This includes public, protected, default (package) access, and private fields, but excludes inherited fields.

This method returns an array of length 0 if the class or interface declares no fields, or if this Class object represents a primitive type, an array class, or void.

Syntax : 
public Field[] getDeclaredFields()  throws SecurityException
Parameters : 
NA
Returns :
the array of Field objects representing all the declared fields of this class
Throws :
SecurityException - If a security manager, s, is present.

// Java program to demonstrate getDeclaredFields() method
  
import java.lang.reflect.Field;
  
public class Test
{
    // some declared fields
    int i;
    String str;
    boolean b;
      
    public static void main(String[] args)
    {
        // returns the Class object associated with Test class
        Class myClass = Test.class;
          
        // getDeclaredFields on myClass
        Field f[] = myClass.getDeclaredFields();
          
        System.out.println("Declared fields present in " +
                                            myClass.getName() + " class are : ");
          
        // iterating through declared fields of Test class
        for (Field field : f) 
        {
            System.out.println(field);
        }
    }
}

Output:

Declared fields present in Test class are : 
int Test.i
java.lang.String Test.str
boolean Test.b

Method getDeclaredMethod(String methodName,Class… parameterTypes) : This method returns a Method object that reflects the specified declared method of the class or interface represented by this Class object.

Syntax : 
public Method getDeclaredMethod(String methodName,Class... parameterTypes) 
throws NoSuchFieldException,SecurityException
Parameters : 
methodName -  the method name
parameterTypes - the list of parameters
Returns :
the Method object for the method of this class matching the specified name and parameters
Throws :
NoSuchMethodException - if a method with the specified name is not found.
NullPointerException - if methodName is null
SecurityException - If a security manager, s, is present.

// Java program to demonstrate getDeclaredMethod() method
  
import java.lang.reflect.Method;
  
public class Test
{
    // any declared method
    // with a String argument
    public void m1(String str)
    {
        System.out.println(str);
    }
      
    public static void main(String[] args) 
            throws NoSuchMethodException, SecurityException, ClassNotFoundException
    {
        // returns the Class object associated with Test class
        Class myClass = Test.class;
          
        // returns the Class object for the class 
        // with the specified name 
        Class c = Class.forName("java.lang.String");
          
        // getDeclaredMethod on myClass
        Method m = myClass.getDeclaredMethod("m1",c);
          
        System.out.println("Declared method present in " +
                                myClass.getName() +
                                " class specified by argument : " + c.getName());
          
        System.out.println(m);
    }
}

Output:

Declared method present in Test class specified by argument : java.lang.String
public void Test.m1(java.lang.String)

Method[] getDeclaredMethods() : This method retuns an array of Method objects reflecting all the methods declared by the class or interface represented by this Class object. This includes public, protected, default (package) access, and private methods, but excludes inherited methods.

This method returns an array of length 0 if the class or interface declares no methods, or if this Class object represents a primitive type, an array class, or void.

Syntax : 
public Method[] getDeclaredMethods() throws SecurityException
Parameters : 
NA
Returns :
the array of Method objects representing all the declared methods of this class
Throws :
SecurityException - If a security manager, s, is present.

// Java program to demonstrate getDeclaredMethods() method
  
import java.lang.reflect.Method;
  
public class Test
{
    // some declared Methods
    public void m1()
    {
        System.out.println("Inside m1 method");
    }
      
    static void m2()
    {
        System.out.println("Inside m2 method");
    }
      
    // main method
    public static void main(String[] args)
    {
        // returns the Class object associated with Test class
        Class myClass = Test.class;
          
        // getDeclaredMethods on myClass
        Method m[] = myClass.getDeclaredMethods();
          
        System.out.println("Declared methods present in " +
                                            myClass.getName() + " class are : ");
          
        // iterating through declared Methods of Test class
        for (Method Method : m) 
        {
            System.out.println(Method);
        }
    }
}

Output:

Declared methods present in Test class are : 
public static void Test.main(java.lang.String[])
public void Test.m1()
static void Test.m2()

Constructor<?> getDeclaredConstructor(Class<?>… parameterTypes) : This method returns a Constructor object that reflects the specified constructor of the class or interface represented by this Class object.

Syntax : 
public Constructor<?> getDeclaredConstructor(Class<?>... parameterTypes) 
throws NoSuchMethodException,SecurityException
Parameters : 
parameterTypes - the list of parameters
Returns :
The Constructor object for the constructor with the specified parameter list
Throws :
NoSuchMethodException - if a Constructor with the specified parameterTypes is not found.
SecurityException - If a security manager, s, is present.

// Java program to demonstrate getDeclaredConstructor() Constructor
  
import java.lang.reflect.Constructor;
  
public class Test
{
      
    public static void main(String[] args) 
            throws NoSuchMethodException, SecurityException, ClassNotFoundException
    {
        // returns the Class object for the class 
        // with the specified name 
        Class c1 = Class.forName("java.lang.Integer");
        Class c2 = Class.forName("java.lang.String");
          
        // getDeclaredConstructor on myClass
        Constructor con = c1.getDeclaredConstructor(c2);
          
        System.out.println("Declared Constructor present in " + c1.getName() + 
                                  " class specified by argument : " + c2.getName());
          
        System.out.println(con);
    }
}

Output:

Declared Constructor present in java.lang.Integer class specified by argument : 
java.lang.String public java.lang.Integer(java.lang.String) 
throws java.lang.NumberFormatException

Constructor<?>[] getDeclaredConstructors() : This method returns an array of Constructor objects reflecting all the constructors declared by the class represented by this Class object. These are public, protected, default (package) access, and private constructors.

This method returns an array of length 0 if this Class object represents an interface, a primitive type, an array class, or void.

Syntax : 
public Constructor<?>[] getDeclaredConstructors() throws SecurityException
Parameters : 
NA
Returns :
the array of Constructor objects representing all the declared constructors of this class
Throws :
SecurityException - If a security manager, s, is present.

// Java program to demonstrate getDeclaredConstructors() Constructor
  
import java.lang.reflect.Constructor;
  
public class Test
{
      
    public static void main(String[] args) 
            throws ClassNotFoundException
    {
        // returns the Class object for the class 
        // with the specified name 
        Class c = Class.forName("java.lang.String");
          
        // getDeclaredConstructors on myClass
        Constructor con[] = c.getDeclaredConstructors();
          
        System.out.println("Declared Constructors present in " +
                                c.getName() + " class are : ");
          
        // iterating through all constructors
        for (Constructor constructor : con) 
        {
            System.out.println(constructor);
        }
    }
}

Output:

Declared Constructors present in java.lang.String class are : 
public java.lang.String(byte[],int,int)
public java.lang.String(byte[],java.nio.charset.Charset)
public java.lang.String(byte[],java.lang.String) throws 
java.io.UnsupportedEncodingException
public java.lang.String(byte[],int,int,java.nio.charset.Charset)
public java.lang.String(byte[],int,int,java.lang.String) 
throws java.io.UnsupportedEncodingException
java.lang.String(char[],boolean)
public java.lang.String(java.lang.StringBuilder)
public java.lang.String(java.lang.StringBuffer)
public java.lang.String(byte[])
public java.lang.String(int[],int,int)
public java.lang.String()
public java.lang.String(char[])
public java.lang.String(java.lang.String)
public java.lang.String(char[],int,int)
public java.lang.String(byte[],int)
public java.lang.String(byte[],int,int,int)

Class<?> getDeclaringClass() : If the class or interface represented by this Class object is a member of another class, then this method returns the Class object representing the class in which it was declared.

This method returns null if this class or interface is not a member of any other class. If this Class object represents an array class, a primitive type, or void,then this method returns null.

Syntax : 
public Class<?>  getDeclaringClass()
Parameters : 
NA
Returns :
the declaring class of this class

// Java program to demonstrate 
// getDeclaringClass() Class
import java.lang.reflect.Method;
public class Test 
{
    // any method
    public void m1()
    {
        System.out.println("Inside m1 method");
    }
      
    public static void main(String[] args) 
    {
          
        // returns A class object
        Class c1 = Test.class;
          
        // getting all methods of Test class
        // Note that methods from Object class
        // are also inherited
        Method m[] = c1.getMethods();
          
        for (Method method : m) 
        {
            // getDeclaringClass method
            // it return declared class of this method
            System.out.println(method.getName() + " is present in " 
                                            + method.getDeclaringClass());
        }
          
    }
}

Output:

main is present in class Test
m1 is present in class Test
wait is present in class java.lang.Object
wait is present in class java.lang.Object
wait is present in class java.lang.Object
equals is present in class java.lang.Object
toString is present in class java.lang.Object
hashCode is present in class java.lang.Object
getClass is present in class java.lang.Object
notify is present in class java.lang.Object
notifyAll is present in class java.lang.Object

Class<?> getEnclosingClass() : This method returns the immediately enclosing class of the underlying class. If the underlying class is a top level class this method returns null.

Syntax : 
public Class<?> getEnclosingClass()
Parameters : 
NA
Returns :
the immediately enclosing class of the underlying class

// Java program to demonstrate getEnclosingClass() Class
  
public class Test
{
    // any inner class of Test class
    class A{}
      
    public static void main(String[] args) 
    {
          
        // returns A class object
        Class c1 = Test.A.class;
          
        // getEnclosingClass method
        // it returns the class object where A class present
        Class c2 = c1.getEnclosingClass();
          
        System.out.println("The class " + c1.getName() + " is present in class : ");
          
        System.out.println(c2);
          
    }
}

Output:

The class Test$A is present in class : 
class Test

Method getEnclosingMethod() : If this Class object represents a local or anonymous class within a method, returns a Method object representing the immediately enclosing method of the underlying class.

Syntax : 
public Class<?> getEnclosingMethod()
Parameters : 
NA
Returns :
the immediately enclosing method of the underlying class,
if that class is a local or anonymous class;
otherwise null

// Java program to demonstrate getEnclosingMethod() method
  
import java.lang.reflect.Method;
  
public class Test
{
    // any method 
    public static Class m1()
    {   
        // any local class in m1
        class A{};
          
        // returning class A
        return A.class;
    }
  
      
    // main method
    public static void main(String[] args) 
            throws ClassNotFoundException
    {
        // returns A Class object
        Class c = Test.m1();
          
        // getEnclosingMethod method
        Method m = c.getEnclosingMethod();
          
        System.out.println("The class " + c.getName() + " is present in method : ");
          
        System.out.println(m);
          
    }
}

Output:

The class Test$1A is present in method : 
public static java.lang.Class Test.m1()

Constructor getEnclosingConstructor() : If this Class object represents a local or anonymous class within a constructor, returns a Constructor object representing the immediately enclosing constructor of the underlying class. Returns null otherwise.

Syntax : 
public Constructor<?> getEnclosingConstructor()
Parameters : 
NA
Returns :
the immediately enclosing constructor of the underlying class,
if that class is a local or anonymous class; 
otherwise null.

// Java program to demonstrate 
// getEnclosingConstructor() Constructor
  
import java.lang.reflect.Constructor;
  
public class Test
{
    Class c;
      
    // default(any) constructor 
    public Test()
    {
        // any local class
        class A{};
          
        // returns A class object
        c = A.class;
    } 
      
    public static void main(String[] args) 
    {
        // creating Test class object
        Test t = new Test();
          
        // getEnclosingConstructor method
        Constructor con = t.c.getEnclosingConstructor();
          
        System.out.println("The class " + t.c.getName() 
                        + " is present in constructor : ");
          
        System.out.println(con);
          
    }
}

Output:

The class Test$1A is present in Constructor : 
public Test()

ProtectionDomain getProtectionDomain() : Returns the ProtectionDomain of this class. If there is a security manager installed, this method first calls the security manager’s checkPermission method with a RuntimePermission(“getProtectionDomain”) permission to ensure it’s ok to get the ProtectionDomain.

Syntax : 
public ProtectionDomain getProtectionDomain()
Parameters : 
NA
Returns :
the ProtectionDomain of this class
Throws :
SecurityException - if a security manager s exists 
and its checkPermission method doesn't allow getting the ProtectionDomain.

// Java program to demonstrate getProtectionDomain() method
public class Test
{
    public static void main(String[] args)
                         throws ClassNotFoundException
    {
        // returns the Class object for the class 
        // with the specified name 
        Class c1 = Class.forName("java.lang.String");
          
        // checking for assertion status of String class
          
        System.out.println("protection domain of " + c1.getName() + " class : ");
          
        // getProtectionDomain() method
        // it will print null as String class is loaded by 
        // BootStrap class loader
        System.out.println(c1.getProtectionDomain());
          
    }
}

Output:

protection domain of java.lang.String class : 
ProtectionDomain  null
 null
 
 java.security.Permissions@7852e922 (
 ("java.security.AllPermission" "" "")
)

boolean isAnnotationPresent(Class<?extends Annotation> annotationClass)() : This method returns true if an annotation for the specified type is present on this element, else false. This method is designed primarily for convenient access to marker annotations.

Specified by:
isAnnotationPresent in interface AnnotatedElement
Syntax : 
public boolean isAnnotationPresent(Class<? extends Annotation> annotationClass) 
Parameters : 
annotationClass - the Class object corresponding to the annotation type
Returns :
true if an annotation for the specified annotation type is present on this element
false, otherwise
Throws:
NullPointerException - if the given annotation class is null

boolean isSynthetic() : This method determines if this class is a synthetic class or not.

Syntax : 
public boolean isSynthetic()
Parameters : 
NA
Returns :
return true if and only if this class is a synthetic class.

URL getResource(String name) : Finds a resource with a given name. The rules for searching resources associated with a given class are implemented by the defining class loader of the class.
```
Syntax : 
public URL getResource(String name)
Parameters : 
name - name of the desired resource
Returns :
A URL object or null if no resource with this name is found
```

InputStream getResourceAsStream(String name) : Finds a resource with a given name. The rules for searching resources associated with a given class are implemented by the defining class loader of the class.

Syntax : 
public InputStream getResourceAsStream(String name)
Parameters : 
name - name of the desired resource
Returns :
A InputStream object or null if no resource with this name is found
Throws:
NullPointerException - If name is null

Object[] getSigners() : Gets the signers of this class.

Syntax : 
public Object[] getSigners()
Parameters : 
NA
Returns :
the signers of this class, or null if there are no signers.
In particular,it returns null if this object represents a primitive type or void.

Annotation[] getAnnotations() : This method returns all annotations present on this element. It returns an array of length zero if this element has no annotations.
The caller of this method is free to modify the returned array; it will have no effect on the arrays returned to other callers.
```
Specified by:
getAnnotations() in interface AnnotatedElement
Syntax : 
public Annotation[] getAnnotations()
Parameters : 
NA
Returns :
all annotations present on this element
```

<A extends Annotation> A getAnnotation(Class<A> annotationClass) : This method returns this element’s annotation for the specified type if such an annotation is present, else null.

Specified by:
getAnnotations() in interface AnnotatedElement
Syntax : 
public Annotation[] getAnnotations()
Parameters : 
annotationClass - the Class object corresponding to the annotation type
Returns :
return element's annotation for the specified annotation type if present on this element
else null
Throws:
NullPointerException - if the given annotation class is null

Annotation[] getDeclaredAnnotations() : Returns all annotations that are directly present on this element. Unlike the other methods in this interface, this method ignores inherited annotations. It returns an array of length zero if no annotations are directly present on this element.
The caller of this method is free to modify the returned array; it will have no effect on the arrays returned to other callers.
```
Specified by:
getDeclaredAnnotations in interface AnnotatedElement
Syntax : 
public Annotation[] getDeclaredAnnotations()
Parameters : 
NA
Returns :
All annotations directly present on this element
```

This article is contributed by Gaurav Miglani. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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My Personal Notes

Mar	APR	May
	17
2020	2021	2022

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