oop - Why can't I create a object in a function in Java? -

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code works well, think code b can work correctly, in fact, code b doesn't work correctly. why?

why can't create object in function- private void setfield(context mcontext,matt afield,string name) ?

code a

public class murlpar {      public matt diskcount=new  matt();     public matt diskindex=new  matt();       public murlpar(context mcontext){         setfield(mcontext,diskcount,"pardiskcount");         setfield(mcontext,diskindex,"pardiskindex");     }       public class matt {         public string name;         public string value;     }       private void setfield(context mcontext,matt afield,string name){         int id = mcontext.getresources().getidentifier(name, "string", mcontext.getpackagename());         afield.name=mcontext.getstring(id);     } }

code b

public class murlpar {      public matt diskcount;      public matt diskindex;       public murlpar(context mcontext){         setfield(mcontext,diskcount,"pardiskcount");         setfield(mcontext,diskindex,"pardiskindex");     }       public class matt {         public string name;         public string value;     }       private void setfield(context mcontext,matt afield,string name){         afield=new matt(); //create object         int id = mcontext.getresources().getidentifier(name, "string", mcontext.getpackagename());         afield.name=mcontext.getstring(id);     } }

what's happening in code b murlpar constructor passes reference diskcount/diskindex setfield, within method has name afield.

you reassign afield reference newly created object, , manipulate object. note afield referring separate object, , not whatever referring when entered setfield.

if you're familiar c can think of you're doing here along these lines:

void setfield(matt *afield) {     afield = (matt*) calloc(1, sizeof(matt)); }  matt *diskcount; setfield(diskcount);

and expecting diskcount have changed after call setfield, won't have.

if want out parameter, can simulate returning newly created object:

private matt setfield(context mcontext, string name){     matt afield = new matt(); //create object     int id = mcontext.getresources().getidentifier(name, "string", mcontext.getpackagename());     afield.name=mcontext.getstring(id);     return afield; }

and then:

diskcount = setfield(mcontext, "pardiskcount");

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