我在接下来的事情上遇到了麻烦：我有一个带有数字的arraylist，我想要反转列表中的数字，如果它有1 2 3，则替换中的值3 2的arraylist 1.为此，我创建了一个名为reordenar（）的方法;它将第一个arraylist中的最后一个数字放在第二个arraylist的第一个位置。完成此操作后，我不知道如何让第一个arraylist将其数字替换为第二个。这是我编写的代码。
package firstPackage;
import java.util.*;
public class firstMain {
public static Object reordenar(List n){
List secondList = new ArrayList();
for (int i=0; i<n.size(); i++){
secondList.add(n.size()-i);
}
return n;
}
public static void main(String[] args) {
// TODO Auto-generated method stub
List firstList = new ArrayList();
firstList.add("1");
firstList.add("2");
firstList.add("3");
firstList.add("7");
firstList.add("5");
firstList.add("6");
firstList.add("9");
reordenar(firstList);
System.out.println(firstList);
}
}
该代码只打印出正常的顺序，而不是重新排列的顺序。非常感谢你的帮助。
答案 0 :(得分：1)
您不需要2 import UIKit
import QuartzCore
enum SlideOutState {
case BothCollapsed
case LeftPanelExpanded
}
class ContainerViewController: UIViewController {
var centerNavigationController: UINavigationController!
var centerViewController: ViewController!
var currentState: SlideOutState = .BothCollapsed {
didSet {
let shouldShowShadow = currentState != .BothCollapsed
showShadowForCenterViewController(shouldShowShadow)
}
}
var leftViewController: SidePanelViewController?
override func viewDidLoad() {
super.viewDidLoad()
centerViewController = UIStoryboard.centerViewController()
centerViewController.delegate = self
// wrap the centerViewController in a navigation controller, so we can push views to it
// and display bar button items in the navigation bar
centerNavigationController = UINavigationController(rootViewController: centerViewController)
view.addSubview(centerNavigationController.view)
addChildViewController(centerNavigationController)
centerNavigationController.didMoveToParentViewController(self)
}
}
let centerPanelExpandedOffset: CGFloat = 60
extension ContainerViewController: CenterViewControllerDelegate {
func toggleLeftPanel() {
let notAlreadyExpanded = (currentState != .LeftPanelExpanded)
if notAlreadyExpanded {
addLeftPanelViewController()
}
animateLeftPanel(shouldExpand: notAlreadyExpanded)
}
func toggleRightPanel() {
}
func addLeftPanelViewController() {
if (leftViewController == nil) {
leftViewController = UIStoryboard.leftViewController()
leftViewController!.categories = Category.allCats()
addChildSidePanelController(leftViewController!)
}
}
func addChildSidePanelController(sidePanelController: SidePanelViewController) {
view.insertSubview(sidePanelController.view, atIndex: 0)
addChildViewController(sidePanelController)
sidePanelController.didMoveToParentViewController(self)
}
func animateLeftPanel(shouldExpand shouldExpand: Bool) {
if (shouldExpand) {
currentState = .LeftPanelExpanded
animateCenterPanelXPosition(targetPosition: CGRectGetWidth(centerNavigationController.view.frame) - centerPanelExpandedOffset)
} else {
animateCenterPanelXPosition(targetPosition: 0) { finished in
self.currentState = .BothCollapsed
self.leftViewController!.view.removeFromSuperview()
self.leftViewController = nil;
}
}
}
func animateCenterPanelXPosition(targetPosition targetPosition: CGFloat, completion: ((Bool) -> Void)! = nil) {
UIView.animateWithDuration(0.5, delay: 0, usingSpringWithDamping: 0.8, initialSpringVelocity: 0, options: .CurveEaseInOut, animations: {
self.centerNavigationController.view.frame.origin.x = targetPosition
}, completion: completion)
}
func showShadowForCenterViewController(shouldShowShadow: Bool) {
if (shouldShowShadow) {
centerNavigationController.view.layer.shadowOpacity = 0.8
} else {
centerNavigationController.view.layer.shadowOpacity = 0.0
}
}
}
private extension UIStoryboard {
class func mainStoryboard() -> UIStoryboard { return UIStoryboard(name: "Main", bundle: NSBundle.mainBundle()) }
class func leftViewController() -> SidePanelViewController? {
return mainStoryboard().instantiateViewControllerWithIdentifier("LeftViewController") as? SidePanelViewController
}
class func centerViewController() -> ViewController? {
return mainStoryboard().instantiateViewControllerWithIdentifier("CenterViewController") as? ViewController
}
}
来完成这项工作。只需迭代你ArrayList的一半元素，并使用临时变量在第一个和最后一个之间交换位置，第二个和第二个形成结尾等。
使用ArrayList而不提供它将包含的特定类型也不是一个好主意：
ArrayList前者（没有特定类型）暗示List<String> firstList = new ArrayList<String>();
代表Object，ArrayList通常太宽而无法使用。