Five ways to create objects in Java

Use the simplest description to differentiate between the new keyword and the Newinstance () method:
Newinstance: Weak type. Low efficiency. Only parameterless constructs can be called.
NEW: Strongly typed. relatively efficient. Can invoke any public construct.

Newinstance () is a method, and new is a keyword, and second, the use of newinstance () under class is limited, because it generates objects that can only invoke parameterless constructors, and the use of the new keyword to generate objects does not have this limitation.
Class.forName ("") returns the class
Class.forName (""). Newinstance () returns an object

As Java developers, we create a lot of objects every day, but we often use dependency management systems like spring to create objects. However, there are many ways to create objects, which we will learn from this article.

There are 5 ways to create objects in Java, with examples of them and their bytecode:

Use the New keyword	}→ called the constructor
Using the class Newinstance method	}→ called the constructor
Using the Newinstance method of the constructor class	}→ called the constructor
Using the Clone method	}→ no constructor is called
Using deserialization	}→ no constructor is called

If you run the program at the end, you will find that method 4,5 creates the object with the constructor, and the method does not call the constructor.

1. Use the New keyword

This is the most common and simplest way to create objects. In this way, we can call any constructor (with no arguments and with parameters).

< Span style= "color: #ff0000;" >employee emp1 = new employee (); </span>

0: new#19          // class org/programming/mitra/exercises/Employee3: dup4: invokespecial #21// Method org/programming/mitra/exercises/Employee."":()V

2. Using the class Newinstance method

We can also use the class class's Newinstance method to create an object. This newinstance method calls the parameterless constructor to create the object.

We can create an object by calling the Newinstance method in the following way:

             Employee emp2 = (Employee) Class.forName( "org.programming.mitra.exercises.Employee" ).newInstance();

Or:

Employee emp2 = Employee.class.newInstance();

　

3. Using the Newinstance method of the constructor class

Like the Newinstance method of class, there is also a newinstance method in the Java.lang.reflect.Constructor class that can create objects. We can call the parameterized and private constructors through this newinstance method.

Constructor<Employee> constructor = Employee.class.getConstructor();

Employee emp3 = constructor.newInstance();

These two newinstance methods are what we call reflection. In fact, class's Newinstance method internally calls constructor's Newinstance method. This is also why many frameworks, such as spring, Hibernate, struts, etc. use the latter.

4. Using the Clone method

Whenever we invoke the Clone method of an object, the JVM creates a new object that copies the contents of the preceding object in its entirety. Creating an object with the Clone method does not call any constructors.

To use the Clone method, we need to implement the Cloneable interface first and implement its definition of the Clone method.

Employee emp4 = (Employee) emp3.clone();

5. Using deserialization

When we serialize and deserialize an object, the JVM creates a separate object for us. When deserializing, the JVM creates an object and does not call any constructors.
In order to deserialize an object, we need to have our class implement the Serializable interface

ObjectInputStream in = newObjectInputStream(newFileInputStream("data.obj"));Employee emp5 = (Employee) in.readObject();

我们从上面的字节码片段可以看到，除了第 1 个方法，其他 4 个方法全都转变为invokevirtual(创建对象的直接方法)，第一个方法转变为两个调用， new 和invokespecial(构造函数调用)。Example

Let's take a look at creating an object for the following employee class:

1 classEmployeeImplementscloneable, Serializable {2     Private Static Final LongSerialversionuid = 1L;3     PrivateString name;4      PublicEmployee () {5System.out.println ("Employee Constructor called ...");6     }7      PublicString GetName () {8         returnname;9     }Ten      Public voidsetName (String name) { One          This. Name =name; A     } - @Override -      Public inthashcode () { the         Final intPrime = 31; -         intresult = 1; -result = Prime * result + ((name = =NULL) ? 0: Name.hashcode ()); -         returnresult; +     } - @Override +      Public Booleanequals (Object obj) { A         if( This==obj) at             return true; -         if(obj = =NULL) -             return false; -         if(GetClass ()! =Obj.getclass ()) -             return false; -Employee other =(Employee) obj; in         if(Name = =NULL) { -             if(Other.name! =NULL) to                 return false; +}Else if(!name.equals (other.name)) -             return false; the         return true; *     } $ @OverridePanax Notoginseng      PublicString toString () { -         return"Employee [name=" + name + "]"; the     } + @Override A      PublicObject Clone () { theObject obj =NULL; +         Try { -obj =Super. Clone (); $}Catch(clonenotsupportedexception e) { $ e.printstacktrace (); -         } -         returnobj; the     } -}

In the following Java program, we will create the employee object in 5 ways.

1  Public classobjectcreation {2      Public Static voidMain (String ... args)throwsException {3         //by using new keyword4Employee EMP1 =NewEmployee ();5Emp1.setname ("Naresh");6System.out.println (Emp1 + ", Hashcode:" +Emp1.hashcode ());7         //by using Class class ' s Newinstance () method8Employee EMP2 = (employee) class.forname ("Org.programming.mitra.exercises.Employee")9 . newinstance ();Ten         //Or We can simply do this One         //Employee emp2 = Employee.class.newInstance (); AEmp2.setname ("Rishi"); -System.out.println (EMP2 + ", Hashcode:" +Emp2.hashcode ()); -         //by using Constructor class ' s newinstance () method theConstructor<employee> Constructor = Employee.class. GetConstructor (); -Employee Emp3 =constructor.newinstance (); -Emp3.setname ("Yogesh"); -System.out.println (Emp3 + ", Hashcode:" +Emp3.hashcode ()); +         //by using Clone () method -Employee Emp4 =(Employee) Emp3.clone (); +Emp4.setname ("Atul"); ASystem.out.println (Emp4 + ", Hashcode:" +Emp4.hashcode ()); at         //by using deserialization -         //Serialization -ObjectOutputStream out =NewObjectOutputStream (NewFileOutputStream ("Data.obj")); - Out.writeobject (emp4); - out.close (); -         //deserialization inObjectInputStream in =NewObjectInputStream (NewFileInputStream ("Data.obj")); -Employee EMP5 =(Employee) in.readobject (); to in.close (); +Emp5.setname ("Akash"); -System.out.println (Emp5 + ", Hashcode:" +Emp5.hashcode ()); the     } *}

The program will output:

Employee Constructor Called... Employee [name=Naresh], hashcode : - 1968815046 Employee Constructor Called... Employee [name=Rishi], hashcode : 78970652 Employee Constructor Called... Employee [name=Yogesh], hashcode : - 1641292792 Employee [name=Atul], hashcode : 2051657 Employee [name=Akash], hashcode : 63313419

Five ways to create objects in Java