How does Java delete eligible data from list

Directory deletes qualified data from list deletes a specific element from list

Delete eligible data from list

In the use of Java language, we often encounter the need to remove some data from list, but beginners often encounter the following pits:

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 5, Size: 4
at java.util.ArrayList.rangeCheck(Unknown Source)
at java.util.ArrayList.get(Unknown Source)
at Main.remove3(Main.java:44)
at Main.main(Main.java:18)

So in this summary 1, there are 1 methods to delete data from list:

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
public class Main {
    public static void main(String[] args) {
        ArrayList<String> strs = new ArrayList<>();
        strs.add("1");
        strs.add("32");
        strs.add("3");
        strs.add("4");
        strs.add("5");
        strs.add("36");
//        remove1(strs);
//        remove2(strs);
//        remove3(strs);
        remove4(strs);
        System.out.println("after");
        printList(strs);
    }
    // Use iterator This is java And Android Often used in source code 1 Method, so it is most recommended 
    public static void remove1(List<String> list) {
        Iterator<String> sListIterator = list.iterator();
        while (sListIterator.hasNext()) {
            String str = sListIterator.next();
            if (str.contains("3")) {
                sListIterator.remove();
            }
        }
    }
    // Delete in reverse order to prevent data subscripts from changing due to deleting intermediate items, which makes data error 
    public static void remove2(List<String> list) {
        for (int i = list.size() - 1; i >= 0; i--) {
            if (list.get(i).contains("3")) {
                list.remove(i);
            }
        }
    }
    //  Sequential deletion, but the subscript and index are processed 
    public static void remove3(List<String> list) {
        for (int i = 0, len = list.size(); i < len; i++) {
            if (list.get(i).contains("3")) {
                list.remove(i);
                len--;
                i--;
            }
        }
    }
    //  Do not directly manipulate the original during traversal list
    public static void remove4(List<String> list) {
        List<String> temp = new ArrayList<>();
        for (String str : list) {
            if (str.contains("3")) {
                temp.add(str);
            }
        }
        list.removeAll(temp);
    }
    public static void printList(List<String> list) {
        for (String str : list) {
            System.out.println(str);
        }
    }
}

If there are other good ways to supplement.

Delete a specific element in list

When the database queried out the data, found that some data is not needed, so here to deal with 1, add a loop list, according to the judgment conditions to delete, there will be an exception.

So the new feature of java8 is used here to delete it.

  List<UserFictitious> list = new ArrayList<>();
        for (int i = 0; i < 50; i++){
            UserFictitious userFictitious = new UserFictitious();
            userFictitious.setUserFictitiousName(String.valueOf(i));
            list.add(userFictitious);
        }
  list.removeIf(item -> item.getUserFictitiousName().equals("1"));
  System.out.println(list);

The underlying source code is deleted according to the characteristics of the iterator, and java8 is only encapsulated into removeIf, simplifying the code.

  default boolean removeIf(Predicate<? super E> filter) {
        Objects.requireNonNull(filter);
        boolean removed = false;
        final Iterator<E> each = iterator();
        while (each.hasNext()) {
            if (filter.test(each.next())) {
                each.remove();
                removed = true;
            }
        }
        return removed;
    }