import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class Sky extends MIDlet implements CommandListener {
        public Form f1,f2,f3;


        public Command c1,c2,c3;
        public Display d;
        public Sky(){
            c1 = new Command("进入游戏",Command.SCREEN,1);
            c2 = new Command("游戏帮助",Command.SCREEN,2);
            c3 = new Command("退出游戏",Command.SCREEN,3);
            f1 = new Form("欢迎进入 恋空游戏");
            f1.append("恋空%……");
            f1.addCommand(c1);
            f1.addCommand(c2);
            f1.addCommand(c3);
            f1.setCommandListener(this);

            f2 = new Form("欢迎使用 恋空帮助");
            f2.append("这是帮助！");
            f2.addCommand(c1);
            f2.addCommand(c3);
            f2.setCommandListener(this);

            f3 = new Form("恋空~~");
            f3.append("游戏加载中……");
            f3.addCommand(c2);
            f3.addCommand(c3);
            f3.setCommandListener(this);

            d =  Display.getDisplay(this);
            
         }
        public void startApp(){
            d.setCurrent(f1);
        }
        public void pauseApp(){}
        public void destroyApp(boolean f){}
        public void commandAction(Command now, Displayable d){
            if(now == c1)
                d.setCurrent(f3);
            if(now == c2)
                d.setCurrent(f2);   
            if(now == c3)
                this.notifyDestroyed();   
            
        }
        

}

红色部分在wtk中报错，不能通过编译


Project settings saved
Building "Test01"
C:\WTK25\apps\Test01\src\Sky.java:42: 找不到符号
符号： 方法 setCurrent(javax.microedition.lcdui.Form)
位置： 类 javax.microedition.lcdui.Displayable
                d.setCurrent(f3);
                 ^
C:\WTK25\apps\Test01\src\Sky.java:44: 找不到符号
符号： 方法 setCurrent(javax.microedition.lcdui.Form)
位置： 类 javax.microedition.lcdui.Displayable
                d.setCurrent(f2);   
                 ^
2 错误
com.sun.kvem.ktools.ExecutionException
Build failed


若是删掉则通过编译，请问哪错了，为什么，十分感谢！

请问在此情况下if-else为何比if快呢，各个条件是相对独立的啊。
另外，我的成员变量d =  Display.getDisplay(this);
你根本没有找到问题所在啊

感谢楼上！