how to close the current application with java code

I'm currently using java code to open and close my desktop application, seems App.close() does't work.

my code:

static string hitestpathstring="xxx//hitest.exe";
static App testApp=new App("hitest");

public static void openApp(){
testApp=App.open(hitestpathstring);
}

public static void closeApp(){
testApp=App.focus(hitestpathstring);
testApp.close():
}

the problem is: App.open() works but close() doesn't.

Any advice is appreciated, thanks in advance.