Question

我在for android中有一个java循环，它运行得很完美，但它只存储到循环中列表中的最后一项。我应该将user_id和lesson_id列入清单吗？我不知道从哪里开始，但这就是我所做的。逻辑工作正常，但它只保存两个变量中列表中的一个项目。

Android Studio代码：

// loop to add every user and lesson selected to watch
String user_id = null;
int lesson_id = 0;

for (int i = 0; i<attendees.size(); i++){
    for (int j = 0; j<lesson_iDs.size(); j++){
         user_id = attendees.get(i);
         lesson_id = lesson_iDs.get(j);
    }
}
// get the date for the classWatch
Calendar localCalendar = Calendar.getInstance(TimeZone.getDefault());
Date currentTime = localCalendar.getTime();

// to show in patient activity (sends to SQLite)
watch = new Watch(currentTime, user_id, lesson_id);

Answer 1

这是正常的吗？如果在循环外部使用user_id和lesson_id，则使用最后的值。你不想做类似的事情：

// loop to add every user and lesson selected to watch
String user_id = null;
int lesson_id = 0;
// get the date for the classWatch
Calendar localCalendar = Calendar.getInstance(TimeZone.getDefault());
Date currentTime = localCalendar.getTime();

for (int i = 0; i<attendees.size(); i++){
    for (int j = 0; j<lesson_iDs.size(); j++){
         user_id = attendees.get(i);
         lesson_id = lesson_iDs.get(j);
         // to show in patient activity (sends to SQLite)
         watch = new Watch(currentTime, user_id, lesson_id);
         // Do something with watch...
    }
}

Answer 2

每次循环运行时，参与者.get（i）和lesson_iDs.get（j）的当前值都存储在两个变量（user_id，lesson_id）中，删除最后存储的值。如果要保留与会者和lesson_id列表的所有值，user_id和lesson_id必须是列表，并且在循环中，您必须向其添加attendees.get（i）和lesson_iDs.get（j）的当前值。 / p>

List<String> user_ids = new ArrayList<>();
List<Integer> lesson_ids = new ArrayList<>();

for (int i = 0; i<attendees.size(); i++){
    for (int j = 0; j<lesson_iDs.size(); j++){
         user_ids.add(attendees.get(i));
         lesson_ids.add(lesson_iDs.get(j));
    }
}

Java for循环只存储最后一个值

2 个答案: