What are all the different ways to create an object in Java

Question

Had a conversation with a coworker the other day about this   There s the obvious using a constructor  but what are the other ways there

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Yes  you can create objects using reflection  For example  String class newInstance   will give you a new empty String object

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Within the Java language  the only way to create an object is by calling its constructor  be it explicitly or implicitly  Using reflection results in a call to the constructor method  deserialization uses reflection to call the constructor  factory methods wrap the call to the constructor to abstract the actual construction and cloning is similarly a wrapped constructor call

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Within the Java language  the only way to create an object is by calling its constructor  be it explicitly or implicitly  Using reflection results in a call to the constructor method  deserialization uses reflection to call the constructor  factory methods wrap the call to the constructor to abstract the actual construction and cloning is similarly a wrapped constructor call

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There is a type of object  which can t be constructed by normal instance creation mechanisms  calling constructors   Arrays  Arrays are created with   A   array   new A len     or   A   array   new A     value0  value1  value2      As Sean said in a comment  this is syntactically similar to a constructor call and internally it is not much more than allocation and zero-initializing  or initializing with explicit content  in the second case  a memory block  with some header to indicate the type and the length   When passing arguments to a varargs-method  an array is there created  and filled  implicitly  too   A fourth way would be   A   array    A    Array newInstance A class  len     Of course  cloning and deserializing works here  too   There are many methods in the Standard API which create arrays  but they all in fact are using one  or more  of these ways

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Also you can use    Object myObj   Class forName  your cClass   newInstance

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Also you can use    Object myObj   Class forName  your cClass   newInstance

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Depends exactly what you mean by create but some other ones are    Clone method Deserialization Reflection  Class newInstance    Reflection  Constructor object

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Cloning and deserialization

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Depends exactly what you mean by create but some other ones are    Clone method Deserialization Reflection  Class newInstance    Reflection  Constructor object

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There are five different ways to create an object in Java  1  Using new keyword   constructor get called Employee emp1   new Employee     2  Using newInstance   method of Class   constructor get called Employee emp2    Employee  Class forName  quot org programming mitra exercises Employee quot                                    newInstance     It can also be written as Employee emp2   Employee class newInstance     3  Using newInstance   method of Constructor   constructor get called Constructor lt Employee gt  constructor   Employee class getConstructor    Employee emp3   constructor newInstance     4  Using clone   method    no constructor call Employee emp4    Employee  emp3 clone     5  Using deserialization    no constructor call ObjectInputStream in   new ObjectInputStream new FileInputStream  quot data obj quot     Employee emp5    Employee  in readObject     First three methods new keyword and both newInstance   include a constructor call but later two clone and deserialization methods create objects without calling the constructor  All above methods have different bytecode associated with them  Read Different ways to create objects in Java with Example for examples and more detailed description e g  bytecode conversion of all these methods  However one can argue that creating an array or string object is also a way of creating the object but these things are more specific to some classes only and handled directly by JVM  while we can create an object of any class by using these 5 ways

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Other ways if we are being exhaustive    On the Oracle JVM is Unsafe allocateInstance   which creates an instance without calling a constructor  Using byte code manipulation you can add code to anewarray  multianewarray  newarray or new   These can be added using libraries such as ASM or BCEL  A version of bcel is shipped with Oracle s Java   Again this doesn t call a constructor  but you can call a constructor as a seperate call

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Also  you can de-serialize data into an object  This doesn t go through the class Constructor      UPDATED   Thanks Tom for pointing that out in your comment   And Michael also experimented      It goes through the constructor of the most derived non-serializable superclass    And when that class has no no-args constructor  a InvalidClassException is thrown upon de-serialization    Please see Tom s answer for a complete treatment of all cases  -  is there any other way of creating an object without using  quot new quot  keyword in java

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using the new operator  thus invoking a constructor  using reflection clazz newInstance    which again invokes the constructor   Or by clazz getConstructor     newInstance      again using a constructor  but you can thus choose which one    To summarize the answer - one main way - by invoking the constructor of the object s class   Update  Another answer listed two ways that do not involve using a constructor - deseralization and cloning

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Depends exactly what you mean by create but some other ones are    Clone method Deserialization Reflection  Class newInstance    Reflection  Constructor object

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We can create an objects in 5 ways    by new operator by reflection  e g  Class forName   followed by Class newInstance    by factory method by cloning by reflection api

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We can also create the object in this way -  String s   Hello     Nobody has discuss it

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There are FIVE different ways to create objects in Java   1  Using  new  keyword   This is the most common way to create an object in Java  Almost 99  of objects are created in this way   MyObject object   new MyObject     normal way   2  By Using Factory Method   ClassName ObgRef ClassName FactoryMethod      Example   RunTime rt Runtime getRunTime     Static Factory Method   3  By Using Cloning Concept   By using clone    the clone   can be used to create a copy of an existing object   MyObjectName anotherObject   new MyObjectName    MyObjectName object   anotherObjectName clone     cloning Object   4  Using  Class forName      If we know the name of the class  amp  if it has a public default constructor we can create an object in this way   MyObjectName object    MyObjectNmae  Class forName  PackageName ClassName   newInstance      Example   String st  String Class forName  java lang String   newInstance      5  Using object deserialization   Object deserialization is nothing but creating an object from its serialized form   ObjectInputStreamName inStream   new ObjectInputStreamName anInputStream    MyObjectName object    MyObjectNmae  inStream readObject

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We can also create the object in this way -  String s   Hello     Nobody has discuss it

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We can create an objects in 5 ways    by new operator by reflection  e g  Class forName   followed by Class newInstance    by factory method by cloning by reflection api

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Within the Java language  the only way to create an object is by calling its constructor  be it explicitly or implicitly  Using reflection results in a call to the constructor method  deserialization uses reflection to call the constructor  factory methods wrap the call to the constructor to abstract the actual construction and cloning is similarly a wrapped constructor call

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From an API user perspective  another alternative to constructors are static factory methods  like BigInteger valueOf     though for the API author  and technically  for real   the objects are still created using a constructor

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You can also clone existing object  if it implements Cloneable    Foo fooClone   fooOriginal clone

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There is a type of object  which can t be constructed by normal instance creation mechanisms  calling constructors   Arrays  Arrays are created with   A   array   new A len     or   A   array   new A     value0  value1  value2      As Sean said in a comment  this is syntactically similar to a constructor call and internally it is not much more than allocation and zero-initializing  or initializing with explicit content  in the second case  a memory block  with some header to indicate the type and the length   When passing arguments to a varargs-method  an array is there created  and filled  implicitly  too   A fourth way would be   A   array    A    Array newInstance A class  len     Of course  cloning and deserializing works here  too   There are many methods in the Standard API which create arrays  but they all in fact are using one  or more  of these ways

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Also  you can de-serialize data into an object  This doesn t go through the class Constructor      UPDATED   Thanks Tom for pointing that out in your comment   And Michael also experimented      It goes through the constructor of the most derived non-serializable superclass    And when that class has no no-args constructor  a InvalidClassException is thrown upon de-serialization    Please see Tom s answer for a complete treatment of all cases  -  is there any other way of creating an object without using  quot new quot  keyword in java

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Depends exactly what you mean by create but some other ones are    Clone method Deserialization Reflection  Class newInstance    Reflection  Constructor object

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Reflection   someClass newInstance

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Reflection will also do the job for you   SomeClass anObj   SomeClass class newInstance      is another way to create a new instance of a class  In this case  you will also need to handle the exceptions that might get thrown

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There are four different ways to create objects in java   A  Using new keyword This is the most common way to create an object in java  Almost 99  of objects are created in this way    MyObject object   new MyObject      B  Using Class forName   If we know the name of the class  amp  if it has a public default constructor we can create an object in this way   MyObject object    MyObject  Class forName  subin rnd MyObject   newInstance      C  Using clone   The clone   can be used to create a copy of an existing object   MyObject anotherObject   new MyObject    MyObject object    MyObject  anotherObject clone      D  Using object deserialization Object deserialization is nothing but creating an object from its serialized form   ObjectInputStream inStream   new ObjectInputStream anInputStream    MyObject object    MyObject  inStream readObject      You can read them from here

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there is also ClassLoader loadClass string  but this is not often used   and if you want to be a total lawyer about it  arrays are technically objects because of an array s  length property  so initializing an array creates an object

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Reflection   someClass newInstance

User · Answer

Within the Java language  the only way to create an object is by calling its constructor  be it explicitly or implicitly  Using reflection results in a call to the constructor method  deserialization uses reflection to call the constructor  factory methods wrap the call to the constructor to abstract the actual construction and cloning is similarly a wrapped constructor call

User · Answer

From an API user perspective  another alternative to constructors are static factory methods  like BigInteger valueOf     though for the API author  and technically  for real   the objects are still created using a constructor

User · Answer

You can also clone existing object  if it implements Cloneable    Foo fooClone   fooOriginal clone

User · Answer

there is also ClassLoader loadClass string  but this is not often used   and if you want to be a total lawyer about it  arrays are technically objects because of an array s  length property  so initializing an array creates an object

User · Answer

From an API user perspective  another alternative to constructors are static factory methods  like BigInteger valueOf     though for the API author  and technically  for real   the objects are still created using a constructor

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Method 1  Using new keyword  This is the most common way to create an object in java  Almost 99  of objects are created in this way   Employee object   new Employee      Method 2  Using Class forName    Class forName   gives you the class object  which is useful for reflection  The methods that this object has are defined by Java  not by the programmer writing the class  They are the same for every class  Calling newInstance   on that gives you an instance of that class  i e  callingClass forName  ExampleClass   newInstance   it is equivalent to calling new ExampleClass     on which you can call the methods that the class defines  access the visible fields etc   Employee object2    Employee  Class forName NewEmployee  newInstance      Class forName   will always use the ClassLoader of the caller  whereas ClassLoader loadClass   can specify a different ClassLoader  I believe that Class forName initializes the loaded class as well  whereas the ClassLoader loadClass   approach doesn   t do that right away  it   s not initialized until it   s used for the first time    Another must read   Java  Thread State Introduction with Example Simple Java Enum Example  Method 3  Using clone    The clone   can be used to create a copy of an existing object   Employee secondObject   new Employee    Employee object3    Employee  secondObject clone      Method 4  Using newInstance   method  Object object4   Employee class getClassLoader   loadClass NewEmployee  newInstance      Method 5  Using Object Deserialization  Object Deserialization is nothing but creating an object from its serialized form      Create Object5    create a new file with an ObjectOutputStream FileOutputStream out   new FileOutputStream      ObjectOutputStream oout   new ObjectOutputStream out       write something in the file oout writeObject object3   oout flush        create an ObjectInputStream for the file we created before ObjectInputStream ois   new ObjectInputStream new FileInputStream  crunchify txt     Employee object5    Employee  ois readObject

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There are FIVE different ways to create objects in Java   1  Using  new  keyword   This is the most common way to create an object in Java  Almost 99  of objects are created in this way   MyObject object   new MyObject     normal way   2  By Using Factory Method   ClassName ObgRef ClassName FactoryMethod      Example   RunTime rt Runtime getRunTime     Static Factory Method   3  By Using Cloning Concept   By using clone    the clone   can be used to create a copy of an existing object   MyObjectName anotherObject   new MyObjectName    MyObjectName object   anotherObjectName clone     cloning Object   4  Using  Class forName      If we know the name of the class  amp  if it has a public default constructor we can create an object in this way   MyObjectName object    MyObjectNmae  Class forName  PackageName ClassName   newInstance      Example   String st  String Class forName  java lang String   newInstance      5  Using object deserialization   Object deserialization is nothing but creating an object from its serialized form   ObjectInputStreamName inStream   new ObjectInputStreamName anInputStream    MyObjectName object    MyObjectNmae  inStream readObject

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there is also ClassLoader loadClass string  but this is not often used   and if you want to be a total lawyer about it  arrays are technically objects because of an array s  length property  so initializing an array creates an object

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Method 1  Using new keyword  This is the most common way to create an object in java  Almost 99  of objects are created in this way   Employee object   new Employee      Method 2  Using Class forName    Class forName   gives you the class object  which is useful for reflection  The methods that this object has are defined by Java  not by the programmer writing the class  They are the same for every class  Calling newInstance   on that gives you an instance of that class  i e  callingClass forName  ExampleClass   newInstance   it is equivalent to calling new ExampleClass     on which you can call the methods that the class defines  access the visible fields etc   Employee object2    Employee  Class forName NewEmployee  newInstance      Class forName   will always use the ClassLoader of the caller  whereas ClassLoader loadClass   can specify a different ClassLoader  I believe that Class forName initializes the loaded class as well  whereas the ClassLoader loadClass   approach doesn   t do that right away  it   s not initialized until it   s used for the first time    Another must read   Java  Thread State Introduction with Example Simple Java Enum Example  Method 3  Using clone    The clone   can be used to create a copy of an existing object   Employee secondObject   new Employee    Employee object3    Employee  secondObject clone      Method 4  Using newInstance   method  Object object4   Employee class getClassLoader   loadClass NewEmployee  newInstance      Method 5  Using Object Deserialization  Object Deserialization is nothing but creating an object from its serialized form      Create Object5    create a new file with an ObjectOutputStream FileOutputStream out   new FileOutputStream      ObjectOutputStream oout   new ObjectOutputStream out       write something in the file oout writeObject object3   oout flush        create an ObjectInputStream for the file we created before ObjectInputStream ois   new ObjectInputStream new FileInputStream  crunchify txt     Employee object5    Employee  ois readObject

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Cloning and deserialization

User · Answer

From an API user perspective  another alternative to constructors are static factory methods  like BigInteger valueOf     though for the API author  and technically  for real   the objects are still created using a constructor

User · Answer

there is also ClassLoader loadClass string  but this is not often used   and if you want to be a total lawyer about it  arrays are technically objects because of an array s  length property  so initializing an array creates an object

User · Answer

There are five different ways to create an object in Java  1  Using new keyword   constructor get called Employee emp1   new Employee     2  Using newInstance   method of Class   constructor get called Employee emp2    Employee  Class forName  quot org programming mitra exercises Employee quot                                    newInstance     It can also be written as Employee emp2   Employee class newInstance     3  Using newInstance   method of Constructor   constructor get called Constructor lt Employee gt  constructor   Employee class getConstructor    Employee emp3   constructor newInstance     4  Using clone   method    no constructor call Employee emp4    Employee  emp3 clone     5  Using deserialization    no constructor call ObjectInputStream in   new ObjectInputStream new FileInputStream  quot data obj quot     Employee emp5    Employee  in readObject     First three methods new keyword and both newInstance   include a constructor call but later two clone and deserialization methods create objects without calling the constructor  All above methods have different bytecode associated with them  Read Different ways to create objects in Java with Example for examples and more detailed description e g  bytecode conversion of all these methods  However one can argue that creating an array or string object is also a way of creating the object but these things are more specific to some classes only and handled directly by JVM  while we can create an object of any class by using these 5 ways

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Other ways if we are being exhaustive    On the Oracle JVM is Unsafe allocateInstance   which creates an instance without calling a constructor  Using byte code manipulation you can add code to anewarray  multianewarray  newarray or new   These can be added using libraries such as ASM or BCEL  A version of bcel is shipped with Oracle s Java   Again this doesn t call a constructor  but you can call a constructor as a seperate call

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There are various ways    Through Class newInstance  Through Constructor newInstance  Through deserialisation  uses the no-args constructor of the most derived non-serialisable base class   Through Object clone  does not call a constructor   Through JNI  should call a constructor   Through any other method that calls a new for you  I guess you could describe class loading as creating new objects  such as interned Strings   A literal array as part of the initialisation in a declaration  no constructor for arrays   The array in a  varargs        method call  no constructor for arrays   Non-compile time constant string concatenation  happens to produce at least four objects  on a typical implementation   Causing an exception to be created and thrown by the runtime  For instance throw null  or    toCharArray   0   Oh  and boxing of primitives  unless cached   of course  JDK8 should have lambdas  essentially concise anonymous inner classes   which are implicitly converted to objects  For completeness  and Paulo Ebermann   there s some syntax with the new keyword as well

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Cloning and deserialization

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This should be noticed if you are new to java  every object has inherited from Object   protected native Object clone   throws CloneNotSupportedException

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using the new operator  thus invoking a constructor  using reflection clazz newInstance    which again invokes the constructor   Or by clazz getConstructor     newInstance      again using a constructor  but you can thus choose which one    To summarize the answer - one main way - by invoking the constructor of the object s class   Update  Another answer listed two ways that do not involve using a constructor - deseralization and cloning

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Reflection   someClass newInstance

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There are various ways    Through Class newInstance  Through Constructor newInstance  Through deserialisation  uses the no-args constructor of the most derived non-serialisable base class   Through Object clone  does not call a constructor   Through JNI  should call a constructor   Through any other method that calls a new for you  I guess you could describe class loading as creating new objects  such as interned Strings   A literal array as part of the initialisation in a declaration  no constructor for arrays   The array in a  varargs        method call  no constructor for arrays   Non-compile time constant string concatenation  happens to produce at least four objects  on a typical implementation   Causing an exception to be created and thrown by the runtime  For instance throw null  or    toCharArray   0   Oh  and boxing of primitives  unless cached   of course  JDK8 should have lambdas  essentially concise anonymous inner classes   which are implicitly converted to objects  For completeness  and Paulo Ebermann   there s some syntax with the new keyword as well

User · Answer

Reflection will also do the job for you   SomeClass anObj   SomeClass class newInstance      is another way to create a new instance of a class  In this case  you will also need to handle the exceptions that might get thrown

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Cloning and deserialization

User · Answer

Reflection   someClass newInstance

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Yes  you can create objects using reflection  For example  String class newInstance   will give you a new empty String object

User · Answer

There are four different ways to create objects in java   A  Using new keyword This is the most common way to create an object in java  Almost 99  of objects are created in this way    MyObject object   new MyObject      B  Using Class forName   If we know the name of the class  amp  if it has a public default constructor we can create an object in this way   MyObject object    MyObject  Class forName  subin rnd MyObject   newInstance      C  Using clone   The clone   can be used to create a copy of an existing object   MyObject anotherObject   new MyObject    MyObject object    MyObject  anotherObject clone      D  Using object deserialization Object deserialization is nothing but creating an object from its serialized form   ObjectInputStream inStream   new ObjectInputStream anInputStream    MyObject object    MyObject  inStream readObject      You can read them from here

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This should be noticed if you are new to java  every object has inherited from Object   protected native Object clone   throws CloneNotSupportedException

[java] What are all the different ways to create an object in Java?

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