multithreading - java: are global variables visible in threads -

if declare global variable in main thread, suppose main thread run new thread, can new thread access global variable in main thread?

"msg" string variable acces

/* simple banner applet.     applet creates thread scrolls    message contained in msg right left    across applet's window. */ import java.awt.*; import java.applet.*; /* <applet code="simplebanner" width=300 height=50> </applet> */  public class appletskel extends applet implements runnable {   string msg = " simple moving banner.";  //<<-----------------variable access   thread t = null;   int state;   boolean stopflag;    // set colors , initialize thread.   public void init() {     setbackground(color.cyan);     setforeground(color.red);   }    // start thread   public void start() {     t = new thread(this);     stopflag = false;     t.start();   }    // entry point thread runs banner.   public void run() {     char ch;      // display banner      for( ; ; ) {       try {         repaint();         thread.sleep(250);         ch = msg.charat(0);         msg = msg.substring(1, msg.length());         msg += ch;         if(stopflag)           break;       } catch(interruptedexception e) {}     }   }    // pause banner.   public void stop() {     stopflag = true;     t = null;   }    // display banner.   public void paint(graphics g) {     g.drawstring(msg, 50, 30);     g.drawstring(msg, 80, 40);   } } 

variables visible several threads tricky. strings, however, immutable, simplifies situation.

it visible, when modified ordinary value available other threads not guaranteed. should make volatile, not cached thread locally. use local variable build new string before assigning msg.

if intend modify stopflag other threads, should volatile.