Various techniques of object creation in Java<\/h3>\n
There are a total of five different methods by which we can instantiate an object. They are as follows:<\/p>\n
- \n
- Using a new keyword<\/li>\n
- Using the newInstance() method of the Class<\/li>\n
- Using the newInstance() method of the constructor class<\/li>\n
- Using clone() method<\/li>\n
- Using deserialization<\/li>\n<\/ul>\n
Let us understand each of these methods individually.<\/p>\n
1. Using the new keyword<\/h4>\n
The new keyword is the most common technique used to instantiate an object. Therefore, the new keyword calls the constructor of the object and creates a new instance of the class.<\/p>\n
Syntax of the new keyword in Java:<\/strong><\/p>\n
ClassName ObjectName = new Class Name();\r\n<\/pre>\n
Code to understand object creation with the new keyword:<\/strong><\/p>\n
package com.DataFlair.ObjectCreation;\r\npublic class NewKeyword\r\n{\r\n void show() \r\n { \r\n System.out.println(\"DataFlair\"); \r\n } \r\n public static void main(String[] args) \r\n { \r\n NewKeyword obj = new NewKeyword();\/\/object creation \r\n obj.show();\/\/Calling method that is part of the object\r\n } \r\n}\r\n\r\n<\/pre>\nThe output of the above code:<\/strong><\/p>\n
DataFlair<\/div>\n2. Using newInstance() Method of Class<\/h4>\n
The newInstance() method of the Class class calls the default constructor to create the object. Hence, the method returns the newly created instance of the class of which the object is a part. However, the newInstance() method is part of the Constructor class.<\/p>\n
- \n
- IllegalAccessException:<\/strong> This exception is thrown when an object does not have the charge of accessing the methods or members of the class that are private.<\/li>\n
- InstantiationException:<\/strong> The instantiation exception in Java usually occurs when an abstract class tries to create its object. As a result, trying to create an object of instant class triggers the behaviour of the abstract class.<\/li>\n
- ExceptionInInitializerError:<\/strong> This error arises when a block or variable that is static throws an exception.<\/li>\n<\/ul>\n
Syntax of newInstance() Method of Class:<\/strong><\/p>\n
public T newInstance() throws InstantiationException, IllegalAccessException \r\n<\/pre>\n
The method throws the following exceptions:<\/strong><\/p>\n
- \n
- IllegalAccessException<\/li>\n
- InstantiationException<\/li>\n
- ExceptionInInitializerError<\/li>\n<\/ul>\n
We can create an object in the following ways:<\/strong><\/p>\n
ClassName object = ClassName.class.newInstance();<\/pre>\n
ClassName object = (ClassName) Class.forName(\"Name of Full Class\").newInstance();<\/pre>\n
The forName() method is a static method that takes a className as a parameter and returns the object of the class. It just loads the class into the program but does not create an object. Thus, if the class cannot be loaded, it gives a ClassNotFoundException and a LinkageError if the linkage has failed.<\/p>\n
The newInstance() method only works if the class has a public default constructor.<\/p>\n
Code to create an object using newInstance() Class class:<\/strong><\/p>\n
package com.DataFlair.ObjectCreation;\r\npublic class InstanceMethodClass\r\n{\r\n String name = \"DataFlair\";\r\n public static void main(String[] args)\r\n {\r\n try\r\n {\r\n Class obj1 = Class.forName(\"com.DataFlair.ObjectCreation.InstanceMethodClass\");\r\n InstanceMethodClass obj =(InstanceMethodClass) obj1.newInstance();\r\n System.out.println(obj.name);\r\n }\r\n catch (Exception e)\r\n {\r\n e.printStackTrace();\r\n }\r\n }\r\n}\r\n<\/pre>\nThe output of the above code:<\/strong><\/p>\n
DataFlair<\/div>\n3. Using newInstance() Method of Constructor class<\/h4>\n
This method is similar to the previous method. It is also known as a reflective way to create an object. The method is defined in the Constructor class of java.lang.reflect package. Unlike the previous method, here we can use parameterized constructors as well as private constructors. This is the reason why this method is preferred over the Class class newInstance() method.<\/p>\n
Syntax of newInstance() Method of the Constructor class in Java:<\/strong><\/p>\n
Public T newInstance(Object... initargs) throws InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException \r\n<\/pre>\n
The newInstance() method passes an array of objects as an argument. It returns a newly created object by calling the constructor of the class.<\/p>\n
The method throws the following exceptions:<\/p>\n
- \n
- IllegalAccessException<\/li>\n
- IllegalArgumentException<\/li>\n
- InstantiationException<\/li>\n
- InvocationTargetException<\/li>\n
- ExceptionInInitializerError<\/li>\n<\/ul>\n
Syntax of creating an object:<\/strong><\/p>\n
Constructor<ClassName> constructor = ClassName.class.getConstructor(); \r\nClassName ObjectName = constructor.newInstance(); \r\n<\/pre>\n
Code to create an object using the Constructor class newInstance() method:<\/strong><\/p>\n
package com.DataFlair.ObjectCreation;\r\nimport java.lang.reflect.*;\r\npublic class InstanceMethodConstructor\r\n{\r\n private String name;\r\n public void Name(String name)\r\n {\r\n this.name = name;\r\n }\r\n public static void main(String[] args)\r\n {\r\n try\r\n {\r\n Constructor<InstanceMethodConstructor> constructor = InstanceMethodConstructor.class.getDeclaredConstructor();\r\n InstanceMethodConstructor obj = constructor.newInstance();\r\n obj.Name(\"DataFlair\");\r\n System.out.println(obj.name);\r\n }\r\n catch (Exception e)\r\n {\r\n e.printStackTrace();\r\n }\r\n }\r\n}\r\n\r\n<\/pre>\nThe output of the above code:<\/strong><\/p>\n
DataFlair<\/div>\n4. Using the clone() Method in Java<\/h4>\n
The clone() method is present inside the Object class. It can create a copy of a preexisting object and return it. It copies the previous object\u2019s properties into the newly created object. The clone() method doesn\u2019t call the constructor. If the object to be copied does not support a cloneable interface, the method will throw CloneNotSupportedException.<\/p>\n
Syntax of clone() Method in Java:<\/strong><\/p>\n
protected Object clone() throws CloneNotSupportedException \r\n<\/pre>\n
Creating a new object from an old object:<\/strong><\/p>\n
ClassName newobjectname = (ClassName) oldobjectname.clone(); \r\n<\/pre>\n
Code to create a new object using the clone() method:<\/strong><\/p>\n
package com.DataFlair.ObjectCreation;\r\npublic class CloneMethod implements Cloneable\r\n{\r\n @Override\r\n protected Object clone() throws CloneNotSupportedException\r\n {\r\n return super.clone();\r\n }\r\n String name = \"DataFlair\";\r\n public static void main(String[] args)\r\n {\r\n CloneMethod obj1 = new CloneMethod();\r\n try\r\n {\r\n CloneMethod obj2 = (CloneMethod) obj1.clone();\r\n System.out.println(obj2.name);\r\n }\r\n catch (CloneNotSupportedException e)\r\n {\r\n e.printStackTrace();\r\n }\r\n }\r\n}\r\n<\/pre>\nThe output of the above code:<\/strong><\/p>\n
- InstantiationException:<\/strong> The instantiation exception in Java usually occurs when an abstract class tries to create its object. As a result, trying to create an object of instant class triggers the behaviour of the abstract class.<\/li>\n
- IllegalAccessException:<\/strong> This exception is thrown when an object does not have the charge of accessing the methods or members of the class that are private.<\/li>\n
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