public class Test {
  private String str;
  public String setStr(String value) {
    if (value != '100$') {this.str = 'go to home, yankers!'}
    else this.str = value;
  }
  public String getStr() {
    return this.str;
  }
}

<script language=JavaScript>
function setStr(value)
{
  if (value != '100$') {this.str = 'go to home, yankers!'}
    else this.str = value;
}
</script>


<form method= "POST"  action= "setStr()" >
  <p><input type= "text"  name= "T1"  size= "20 "></p>
</form>