扫描仪类出现问题

Question

I'm preparing a Project in JAVA for my Computer Applications Internal Assessment and I got an error in calling the method despite the class has no Syntax errors spotted. this is my code:

    package CommandPromptBrowser.GoogleWebsite;
    import java.util.*;
    class Commandprompt
    {
    Scanner sc=new Scanner(System.in);
    Searchbox se=new Searchbox();
    Title ti=new Title();
    Searchresults sr=new Searchresults();
    String cmd;
    String key;
    void commandBox()
    {
        System.out.println("***");
        cmd=sc.next();
        key=sc.next();
    }  
    boolean typeCommand()
    {
        if(cmd.equals("type>box"))
        {
            return(true);
        }
        else 
        {
            return(false);
        }
    }
    boolean clickCommand()
    {
        if(cmd.equals("click>button"))
        {
            if(key.equals(se.search))
            {
                return(true);
            }
            else
            {
                return(false);
            }
        }
        else
        {
            return(false);
        }
    }
    void commands()
    {
        boolean res;
        if(res=typeCommand())
        {
            se.searchBox(key);
            commandBox();
        }
        else if(res=clickCommand())
        {
            sr.resultScreen();
            commandBox();
        }
    }
}

If I call a method called Googleclient,I get the following error:

java.lang.StackOverflowError:
null(in java.lang.String)

and I think that the trouble is due to the Scanner class object. I would like to mention the code of the class Googleclient-

    package CommandPromptBrowser.GoogleWebsite;
public class Googleclient
{
    Title ti=new Title();
    Searchbox sea=new Searchbox();
    Commandprompt cp=new Commandprompt();
    public void clientRunner()
    {
        ti.welcomeScreenTitle();
        sea.emptySearchBox();
        cp.commandBox();
        cp.clickCommand();
        cp.typeCommand();
        cp.commands();
    }
}

Please reply as fast as possible.Please.....

Answer 1

If "cmd" is null, this will fail (null hasn't equals method):

if(cmd.equals("type>box"))

Try to replace it with:

if("type>box".equals(cmd))