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Java Forum / General / April 2007instance of a class in a static context??
How can I create an instance of a class in a static context? I am a newbie, please point me the right direction. My code looks like: public Class1 { // instance of another class Class2 c2; public Class1(Class2 c2) { this.c2 = c2; <code> } public static void main(String[] args, Class2 c2) { //The next line is not allowed, I know , but what is the solution? this.c2 = c2; Class1 c1 = new Class1(c2); <code> c1.setVisible(true); } } I checked the books and surfed the net, but did not find the right answer. Thanks, > How can I create an instance of a class in a static context? > I am a newbie, please point me the right direction. [quoted text clipped - 21 lines] > answer. > Thanks, Class1.c2 = c2; [...] >>public Class1 { >> // instance of another class [quoted text clipped - 3 lines] >> <code> >> } [...] > Class1.c2 = c2; c2 isn't static so you can't do that. > How can I create an instance of a class in a static context? > I am a newbie, please point me the right direction. [quoted text clipped - 20 lines] > answer. > Thanks, I'm not sure what you're trying to achieve and what you mean by static context. In your case c2 ([3]) is not static so [1] is not necessary at all because you initiate c2 in your constructor [2] tlas wClass1.c2 = c2; c2 isn't static so you can't do that. right, it doesn't work. public static void main [...] , this is what I mean by a static context. I try to set visible Class1. The more complete line is code is: public Class1 extends JFrame [...] > wClass1.c2 = c2; > c2 isn't static so you can't do that. [quoted text clipped - 9 lines] > > public Class1 extends JFrame [...] So all you have to do (and in fact you did that) is: Class1 c1 = new Class1(c2); c1.setVisible(true); tlas dendeezen wrote: >> How can I create an instance of a class in a static context? >> I am a newbie, please point me the right direction. >> My code looks like: >> >> public Class1 { Not a very good class name. java.lang.Class already exists, and your class is not similar to it. Try a name like "Example1". You forgot the keyword 'class'. >> // instance of another class >> Class2 c2; //[3] [quoted text clipped - 3 lines] >> } >> public static void main(String[] args, Class2 c2) { This is not the signature for main(). The "real" main() only has one argument. You will not be able to run this class from the command line. Go ahead and create a test instance of Example2 inside your main() method instead of trying to pass it in. >> //The next line is not allowed, I know , but what is >> the solution? >> this.c2 = c2; //[1] That's because 'this' doesn't exist in a static context. You have to create an instance of Example1. >> Class1 c1 = new Class1(c2); >> <code> >> c1.setVisible(true); Now do not write GUI code at this stage, it only complicates things. There is no 'setVisible()' because there is no GUI, so it will fail to compile. >> } >> } You have to create an instance of the class to reference anything not static. ******** class Example2 { public String getName() { return "example 2"; } } public class Example1 { private Example2 eg; public Example1( Example2 e2 ) { this.eg = e2; } public final Example2 getEg() { return eg; } public static void main( String [] args ) { Example2 e2 = new Example2(); Example1 e1 = new Example1( e2 ); System.out.println( "Example1 has an Example2 named \""+ e1.getEg().getName() +"\"." ); } }  SignatureLew Lew, The public class Class1 alias Example1 worked fine until I tried to intantiate Class2 alias Example2. I still don't succeed to get my 'real' code running, ... but I keep on trying.. regards, > The public class Class1 alias Example1 worked fine until I tried to > intantiate Class2 alias Example2. > > I still don't succeed to get my 'real' code running, ... but I keep on > trying.. What code did you use to instantiate Example2? Did it look like this: Example2 e2 = new Example2(); ? If not, that could be your problem. The code you posted had the Class2 passed in as an argument to main(), which would not work. This was mentioned to you. You aren't still doing that, are you? What exactly are you doing? If you provide an SSCCE we can help. If you insist on keeping your problem a secret there's nothing we can do to help you. Provide an SSCCE. SignatureLew > How can I create an instance of a class in a static context? > I am a newbie, please point me the right direction. [quoted text clipped - 21 lines] > answer. > Thanks, Your main function is static so it does not have access to instance variables for that class... The question you can ask yourself is what kind of variables does it have access to. The answer is local variables and class variables. You're already using a local variable c1. So you can do either Class Class1 static Class2 c2; public static void main(String[] args) { c2 = new Class2(); Class1 c1 = new Class1(c2); ... Or Class Class1 public static void main(String[] args) { Class2 c2 = new C2(); Class1 c1 = new Class1(c2); ... When you invoke the Class1 constructor [which I didn't copy], it will link c2 appropriately within c1. Unless there's something special going on, the second alternative is likely what you want. You were almost there with the code you poster but didn't recognize that you can create c2 before you associate it with c1. Regards, Tom McGlynn Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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