Can I use Class newInstance with constructor arguments

Question

I would like to use Class newInstance   but the class I am instantiating does not have a nullary constructor  Therefore I need to be able to pass in constructor arguments  Is there a way to do this

User · Answer

MyClass class getDeclaredConstructor String class  newInstance  HERESMYARG      or  obj getClass   getDeclaredConstructor String class  newInstance  HERESMYARG

User · Answer

You can use the getDeclaredConstructor method of Class  It expects an array of classes  Here is a tested and working example   public static JFrame createJFrame Class c  String name  Component parentComponent        try               JFrame frame    JFrame c getDeclaredConstructor new Class    String class   newInstance  name            if  parentComponent    null                        frame setDefaultCloseOperation JFrame EXIT ON CLOSE                     else                       frame setDefaultCloseOperation JFrame DISPOSE ON CLOSE                     frame setLocationRelativeTo parentComponent           frame pack            frame setVisible true             catch  InstantiationException instantiationException                ExceptionHandler handleException instantiationException  parentComponent  Language messages get Language InstantiationExceptionKey   c getName               catch NoSuchMethodException noSuchMethodException                  ExceptionHandler handleException noSuchMethodException  parentComponent  Language NoSuchMethodExceptionKey   NamedConstructor            ExceptionHandler handleException noSuchMethodException  parentComponent  Language messages get Language NoSuchMethodExceptionKey     Constructor or a JFrame method               catch  IllegalAccessException illegalAccessException                ExceptionHandler handleException illegalAccessException  parentComponent  Language messages get Language IllegalAccessExceptionKey              catch  InvocationTargetException invocationTargetException                ExceptionHandler handleException invocationTargetException  parentComponent  Language messages get Language InvocationTargetExceptionKey              finally               return null

User · Answer

Do not use Class newInstance    see this thread  Why is Class newInstance   evil   Like other answers say  use Constructor newInstance   instead

User · Answer

myObject getClass   getDeclaredConstructors types list  newInstance args list     Edit  according to the comments seems like pointing class and method names is not enough for some users  For more info take a look at the documentation for getting constuctor and invoking it

User · Answer

You can get other constructors with getConstructor

User · Answer

Assuming you have the following constructor  class MyClass       public MyClass Long l  String s  int i               You will need to show you intend to use this constructor like so   Class classToLoad   MyClass class   Class   cArg   new Class 3     Our constructor has 3 arguments cArg 0    Long class    First argument is of  object  type Long cArg 1    String class    Second argument is of  object  type String cArg 2    int class    Third argument is of  primitive  type int  Long l   new Long 88   String s    text   int i   5   classToLoad getDeclaredConstructor cArg  newInstance l  s  i

User · Answer

Follow below steps to call parameterized consturctor    Get Constructor with parameter types by passing types in  Class   for getDeclaredConstructor method of Class Create constructor instance by passing values in Object   for newInstance method of Constructor   Example code   import java lang reflect     class NewInstanceWithReflection      public NewInstanceWithReflection            System out println  Default constructor              public NewInstanceWithReflection  String a           System out println  Constructor  String   gt    a             public static void main String args    throws Exception            NewInstanceWithReflection object    NewInstanceWithReflection Class forName  NewInstanceWithReflection   newInstance            Constructor constructor   NewInstanceWithReflection class getDeclaredConstructor  new Class    String class            NewInstanceWithReflection object1    NewInstanceWithReflection constructor newInstance new Object    StackOverFlow                output   java NewInstanceWithReflection Default constructor Constructor  String   gt  StackOverFlow

User · Answer

Follow below steps to call parameterized consturctor    Get Constructor with parameter types by passing types in  Class   for getDeclaredConstructor method of Class Create constructor instance by passing values in Object   for newInstance method of Constructor   Example code   import java lang reflect     class NewInstanceWithReflection      public NewInstanceWithReflection            System out println  Default constructor              public NewInstanceWithReflection  String a           System out println  Constructor  String   gt    a             public static void main String args    throws Exception            NewInstanceWithReflection object    NewInstanceWithReflection Class forName  NewInstanceWithReflection   newInstance            Constructor constructor   NewInstanceWithReflection class getDeclaredConstructor  new Class    String class            NewInstanceWithReflection object1    NewInstanceWithReflection constructor newInstance new Object    StackOverFlow                output   java NewInstanceWithReflection Default constructor Constructor  String   gt  StackOverFlow

User · Answer

You can get other constructors with getConstructor

User · Answer

MyClass class getDeclaredConstructor String class  newInstance  HERESMYARG      or  obj getClass   getDeclaredConstructor String class  newInstance  HERESMYARG

User · Answer

Do not use Class newInstance    see this thread  Why is Class newInstance   evil   Like other answers say  use Constructor newInstance   instead

User · Answer

Assuming you have the following constructor  class MyClass       public MyClass Long l  String s  int i               You will need to show you intend to use this constructor like so   Class classToLoad   MyClass class   Class   cArg   new Class 3     Our constructor has 3 arguments cArg 0    Long class    First argument is of  object  type Long cArg 1    String class    Second argument is of  object  type String cArg 2    int class    Third argument is of  primitive  type int  Long l   new Long 88   String s    text   int i   5   classToLoad getDeclaredConstructor cArg  newInstance l  s  i

User · Answer

MyClass class getDeclaredConstructor String class  newInstance  HERESMYARG      or  obj getClass   getDeclaredConstructor String class  newInstance  HERESMYARG

User · Answer

I think this is exactly what you want  http   da2i univ-lille1 fr doc tutorial-java reflect object arg html  Although it seems a dead thread  someone might find it useful

User · Answer

myObject getClass   getDeclaredConstructors types list  newInstance args list     Edit  according to the comments seems like pointing class and method names is not enough for some users  For more info take a look at the documentation for getting constuctor and invoking it

User · Answer

Do not use Class newInstance    see this thread  Why is Class newInstance   evil   Like other answers say  use Constructor newInstance   instead

User · Answer

Do not use Class newInstance    see this thread  Why is Class newInstance   evil   Like other answers say  use Constructor newInstance   instead

User · Answer

You can get other constructors with getConstructor

User · Answer

myObject getClass   getDeclaredConstructors types list  newInstance args list     Edit  according to the comments seems like pointing class and method names is not enough for some users  For more info take a look at the documentation for getting constuctor and invoking it

User · Answer

MyClass class getDeclaredConstructor String class  newInstance  HERESMYARG      or  obj getClass   getDeclaredConstructor String class  newInstance  HERESMYARG

User · Answer

myObject getClass   getDeclaredConstructors types list  newInstance args list     Edit  according to the comments seems like pointing class and method names is not enough for some users  For more info take a look at the documentation for getting constuctor and invoking it

User · Answer

You can use the getDeclaredConstructor method of Class  It expects an array of classes  Here is a tested and working example   public static JFrame createJFrame Class c  String name  Component parentComponent        try               JFrame frame    JFrame c getDeclaredConstructor new Class    String class   newInstance  name            if  parentComponent    null                        frame setDefaultCloseOperation JFrame EXIT ON CLOSE                     else                       frame setDefaultCloseOperation JFrame DISPOSE ON CLOSE                     frame setLocationRelativeTo parentComponent           frame pack            frame setVisible true             catch  InstantiationException instantiationException                ExceptionHandler handleException instantiationException  parentComponent  Language messages get Language InstantiationExceptionKey   c getName               catch NoSuchMethodException noSuchMethodException                  ExceptionHandler handleException noSuchMethodException  parentComponent  Language NoSuchMethodExceptionKey   NamedConstructor            ExceptionHandler handleException noSuchMethodException  parentComponent  Language messages get Language NoSuchMethodExceptionKey     Constructor or a JFrame method               catch  IllegalAccessException illegalAccessException                ExceptionHandler handleException illegalAccessException  parentComponent  Language messages get Language IllegalAccessExceptionKey              catch  InvocationTargetException invocationTargetException                ExceptionHandler handleException invocationTargetException  parentComponent  Language messages get Language InvocationTargetExceptionKey              finally               return null

User · Answer

You can get other constructors with getConstructor

User · Answer

I think this is exactly what you want  http   da2i univ-lille1 fr doc tutorial-java reflect object arg html  Although it seems a dead thread  someone might find it useful

[java] Can I use Class.newInstance() with constructor arguments?

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