java方法toArray()不处理列表
我正在尝试将列表转换为数组,但出现了一个错误,我不知道为什么。我以当前小时为单位,在一个for循环中,我得到了今天剩余的时间,并将其放入一个列表中。当我尝试将其更改为数组时,我得到一个错误。我尝试这样做是因为后来我在JCombobox
中使用该数组
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.GregorianCalendar;
import java.util.Calendar;
public class Frame extends JFrame implements ActionListener{
//JFrame elements
private JButton btnSetTime;
private JLabel lblTitle;
private JComboBox comboTime;
//Standard elements
private Timer tillPopup, tillShutdown;
Calendar calendar = new GregorianCalendar();
int hour = (calendar.get(Calendar.HOUR_OF_DAY));
List times = createDropdown(hour);
// Convert ArrayList to array which can be used in the combobox
String[] dropdownElements = times.toArray();
String[] a = {"a","b"};
public Frame(){
setLayout(new FlowLayout());
//Labels
lblTitle = new JLabel("Deze applicatie sluit u computer automatisch af om het energieverbruik te verminderen.");
//Combobox
comboTime = new JComboBox(a);
comboTime.setSelectedIndex(0);
//Button
btnSetTime = new JButton("Zet afsluittijd");
//Timers
//tillPopup = new Timer(this);
//tillShutdown = new Timer(this);
//Add elements to Frame
add(lblTitle);
add(comboTime);
add(btnSetTime);
//Add actionListeners
btnSetTime.addActionListener(this);
setSize(500,300);
setVisible(true);
setDefaultCloseOperation(EXIT_ON_CLOSE);
}
private List createDropdown(int hour){
List availableHours = new List();
for(int i = hour; i <=24; i++){
if (i != 24){
availableHours.add(i + ":00");
}
else if(i == 24){
availableHours.add("00:00");
}
}
return availableHours;
}
public void actionPerformed(ActionEvent e){
if (e.getSource() == btnSetTime){
Object popupTime = comboTime.getSelectedItem();
System.out.println(popupTime);
}
}
}
我得到以下错误:
Frame.java:21: error: cannot find symbol
String[] dropdownElements = times.toArray();
^
symbol: method toArray()
location: variable times of type List
如何将从method createDropdown
返回的列表更改为数组,以及为什么我做错了
# 1 楼答案
由于已导入
import java.awt.*;
,因此使用的List
是java.awt.List
。您需要添加导入-java.util.List
请不要使用原始类型
List
。在较新的代码中不建议使用原始类型。当然,您不可能注意到它,因为java.awt.List
是一个非泛型类。所以即使是编译器也不会给你一个警告信息在您的案例中,应该使用参数化类型-
List<String>
。将您的方法修改为:您还需要添加
import java.util.ArrayList