问题描述
我是一名初学者，几天来我一直在尝试调试我的代码，以找出为什么我在 isDuplicate 中的循环似乎无法正常工作。我已经在网站上搜索了一些想法，但似乎没有一个能解决我的问题。
目标是让用户输入一个项目，然后调用该方法来检查该项目是否已经在数组中。如果不是，则应添加。如果是重复的，应该给出错误信息。
我只能为此使用循环，因为目标是学习 Java 中各种循环的实现。
当我运行程序时，它说第一个输入的项目是重复的。没有发现每个后续项目输入都是重复的。我的 for 循环迭代或我忽略的 if 语句中似乎存在逻辑错误。
任何建议都非常感谢。我整个星期都在尝试在书籍和网上寻找答案，但遇到了障碍。
/*
Grocery List that accepts input,sorts by item name,checks for duplicates and outputs list to user.
*/
public class Main {
private static Scanner input = new Scanner(system.in);
public static void main(String[] args) {
int count = 0; // Number of items currently in the grocery list
String[] groceryList = new String[6];
/*
invoke method to check for duplicate entries.
use while loop for input from user
*/
while (count < groceryList.length) {
System.out.print("Enter a grocery item: ");
String item = input.nextLine();
isDuplicate(item,groceryList,count);
groceryList[count] = item;
count++;
}
// sort elements and use for-each loop to print list
Arrays.sort(groceryList);
System.out.println("Your Grocery List: ");
for (String food : groceryList) {
System.out.println(food);
}
}
/*
I kNow there is an issue with my loop but I Could not figure it out.
Says first element is duplicate but no others.
Cannot use collections. can only use for loops for this method.
*/
public static boolean isDuplicate(String item,String[] list,int listcnt) {
for (listcnt = 0; listcnt < list.length; listcnt++) {
for (int j = listcnt + 1; j < list.length; j++) {
if (list[j] == list[listcnt])
System.out.println("Sorry," + item + " is a duplicate.");
return true;
}
}
return false;
}
}
解决方法
暂时忘掉 Java 代码，从逻辑上思考它，然后在脑海中想出一个算法。
您有一个项目 - 尚未在列表中（这很重要）。您有一个项目列表。您想查看该项目是否已在项目列表中。
你会如何为纸上的列表做这个？
- 扫描项目列表？听起来不错
- 这是否需要遍历列表两次？没有
您也不检查 isDuplicate 检查的结果并始终添加项目
isDuplicate(item,groceryList,count);
groceryList[count] = item;
通常在 Java 中，我们不使用 == 来比较对象：https://www.geeksforgeeks.org/difference-equals-method-java/
if (list[j] == list[i])
您的主要问题是您没有使用 isDuplicate() 的结果：
/*
Grocery List that accepts input,sorts by item name,checks for duplicates and outputs list to user.
*/
public class Main {
public static void main(String... args) {
String[] groceryList = readGroceryList(6);
// sort elements and use for-each loop to print list
Arrays.sort(groceryList);
print(groceryList);
}
private static String[] readGroceryList(int total) {
Scanner scan = new Scanner(System.in);
String[] groceryList = new String[total];
int count = 0; // Number of items currently in the grocery list
/*
invoke method to check for duplicate entries.
use while loop for input from user
*/
while (count < groceryList.length) {
System.out.print("Enter a grocery item: ");
String item = scan.nextLine();
if (isDuplicate(item,count))
System.err.println("Sorry," + item + " is a duplicate.");
else
groceryList[count++] = item;
}
return groceryList;
}
private static void print(String[] groceryList) {
System.out.println("Your Grocery List: ");
for (String food : groceryList)
System.out.println(food);
}
/*
I know there is an issue with my loop but I could not figure it out.
Says first element is duplicate but no others.
Cannot use collections. can only use for loops for this method.
*/
public static boolean isDuplicate(String item,String[] groceryList,int count) {
for (int i = 0; i < count; i++)
if (item.equals(groceryList[i]))
return true;
return false;
}
}
我不明白您的 isDuplicate() 方法。以下是扫描数组中重复项的标准方法：
public static boolean isDuplicate(String item,String[] list){
//iterate the array
for(String listItem : list){
//check if "item" matches "listItem"
if(item.equals(listItem)){
return true;
}
//NOTE: if you want this to not be case sensetive,//e.g. if you want "somestring" to be equal to "SomeString",do
// if(item.equalsIgnoreCase(listItem)){
// return true;
// }
}
//we only get this far in the method if the item is not in the list
return false;
}