java - Custom addToDisplay method returns exception in another class -
a newcomer here. having trouble method prints text jtextarea
.
the addtodisplay
method works fine in native gamewindow
class. here is:
public class gamewindow extends jframe implements keylistener { jtextarea displayarea; public gamewindow() { ... this.addtodisplay(""); //works fine } public void addtodisplay(string newstring) { displayarea.append("\n" + newstring); displayarea.selectall(); } }
when method called in class of same package, throws java.lang.nullpointerexception
public class duelist { private gamewindow window; public duelist(string n) { ... } public void dueling(duelist opponent) { ... window.addtodisplay(""); //exception occurs here } }
please show me how rid of exception. if need more information, let me know in comments.
you have initialize gamewindow
in duelist class before using
gamewindow window=new gamewindow();
for ex in constructor or wherever want before calling methods
public duelist(string n) { window=new gamewindow(); ... }
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