从 ArrayList 中移除一个对象

Question

这里是 java 新手，我无法理解数组。我需要从ArrayList 中删除一个项目，我不知道如何实际编码。我的程序读取一个.csv 文件，从主类传递一个字符串到第二个类，一旦在第二个类中，我需要搜索数组列表并删除该字符串，如果找到它并返回true，表示它已被删除。任何帮助表示赞赏。

二等

public class PersonLogImpl {

private boolean remove;
private boolean isLicenseUnique;
private boolean add;
private final ArrayList<Person> person;

public PersonLogImpl() {
    this.person = new ArrayList<>();
}


public ArrayList<Person> getPersonLog(){
    return Person;
}

public boolean add(Person obj){  //add person object to ordered list 
   person.add(obj);

   return add;
}

public boolean remove (String license){ //remove person with specific license from list

    if(person.remove(person.equals(add))){
            remove = true;
    }
   return remove;
}

编辑： 人物类

public class Person{
private String licenseNumber;

public Person(){

}

public Person(String licenseNumber){
    this.licenseNumber = licenseNumber;
}

public String getLicenseNumber(){
    return licenseNumber;
}

public void setLicenseNumber(String licenseNumber){
    this.licenseNumber = licenseNumber;
}

@Override
public int hashCode(){
    int hash = 7;
    return hash;
}

@Override
public boolean equals(Object obj){
    if (this == obj){
        return true;
    }
    if (obj == null){
        return false;
    }
    if (getClass() != obj.getClass()){
        return false;
    }
    final Person other = (Person) obj;
    if (!Objects.equals(this.licenseNumber, other.licenseNumber)){
        return false;
    }
    return true;
}

@Override
public String toString(){
    return "Person{" + "licenseNumber=" + licenseNumber + '}';
}

public boolean validateLicense(){
    boolean retValue = false;
    if ((this.licenseNumber.matches("^[a-zA-Z]{2}\\d{7}$")))
        retValue = true;
    return retValue;
}

Answer 1

试试这个：

public boolean remove (String license){ //remove person with specific license from list
    Iterator<Person> personIterator = person.iterator();
    boolean remove = false;

    while(personIterator.hasNext(){
        Person personInstance = personIterator.next();  
        if(personInstance.getLicense().equals(license))){
            personIterator.remove();
            remove = true;
            break;
        }
    }

   return remove;
}

Answer 2

@Newb2Java，equals 方法可以将 person 与任何对象进行比较，但如果参数（此处为 add）与调用者（person）的类型不同，则结果是false。尽管您使用了单数名词person，但它的类型是复数，是Persons 的集合。 ArrayList<Person> 永远不会等于 Boolean（也不等于 boolean）。 List 方法 add 将返回 true。 remove 将返回 true 如果它实际上删除了参数，它必须是 Person 类型。首先，您必须找到列表中的哪个元素具有指定的属性值。因此，您必须遍历列表，最好使用迭代器，直到找到具有给定License 的元素的每个实例。像这样的：

package practice;

import java.util.ArrayList;
import java.util.List;
import java.util.ListIterator;

public class Personator {
  private final List<Person> persons = new ArrayList<>();

  public List<Person> getPersons() {
    return new ArrayList<>(persons);
  }

  public boolean add(Person person) {
    return persons.add(person);
  }

  public boolean remove(String license) {
    return remove(new Person(license));
  }

  public boolean remove(Person removal) {
    boolean wasRemoved = false;
    for (ListIterator<Person> iterator = persons.listIterator(persons.size());
       iterator.hasPrevious();
       ) {
      final Person person = iterator.previous();
      if (removal.equals(person)) {
        iterator.remove();
        wasRemoved = true;
      }
    }
    return wasRemoved;
  }
}

用这个：

public class Person {
  private final String license;

  public Person(String license) {
    if (license == null) {
      throw new IllegalArgumentException("null license not allowed");
    }
    this.license = license;
  }

  public String getLicense() {
    return license;
  }

  @Override
  public String toString() {
    return "Person " + getLicense();
  }

  @Override
  public int hashCode() {
    return getLicense().hashCode();
  }

  @Override public boolean equals(Object oth) {
    if (this == oth) {
      return true;
    }
    if (! (oth instanceof Person)) {
      return false;
    }
    Person other = (Person) oth;
    return this.getLicense().equals(other.getLicense());
  }
}

Answer 3

您的代码中有一些错误，我在下面用 cmets 突出显示了它们：

public class PersonLogImpl {
    private boolean remove;
    private boolean isLicenseUnique;
    private boolean add;
    private final ArrayList<Person> person;

    public PersonLogImpl() {
        // YOU SHOULD ALSO ASSIGN THE PRIVATE BOOLEANS HERE
        this.person = new ArrayList<>();
    }

    public ArrayList<Person> getPersonLog() {

        return Person; // What's going on here?
        // You're returning the actual Person class when you should be returning
        // an ArrayList of type Person (I think you meant for the P to be lowercase)
    }

    public boolean add(Person obj){  //add person object to ordered list 
       person.add(obj);

       return add; // You never assign true or false to 'add' (I believe 
       // it defaults to true) so this method will always return true (maybe 
       // false, not sure). you should instead use 'return person.add(obj);'
    }

    public boolean remove (String license){ //remove person with specific license from list

        // The code below makes no sense (no offence).
        if(person.remove(person.equals(add))){
                remove = true;
        }
       return remove;

        // Since I don't know the make up of the 'Person' class I can't 
        // tell you how this method should function. I'll make a guess though:
       for(int i = 0; i < person.size(); ++i) {
           if(person.get(i).getLicenseNumber().equals(license)) {
               return person.remove(i);
           }
       }

       // OR a shorter alternative
       return person.remove(new Person(license));
    }

}

Answer 4

如果您还没有，请在您的 Person 类上创建一个方法 getLicense()。该方法应该返回 Person 的许可证，然后您可以使用下面的 remove 方法；

编辑：我现在看到您的 Person 类上有一个 getLicenseNumber() 方法。

public boolean remove(String license) {
   for (Person individual : person) { // go through each Person on the ArrayList
       if (individual.getLicenseNumber().equals(license)) // check if that Person's license is equal to the license we're looking for
           return person.remove(individual); // if so, remove that person and return true (remove will return true if the element is found)
   }

   return false; // if we never removed any element we never found a person with that license. In that case, return false
}

我假设每个人都有一个唯一的许可证号，并且您不会将同一个 Person 两次添加到 ArrayList 中（或者会阻止用户尝试添加）。 如果您希望删除任何具有该许可证的人员，您可以使用以下方法：

public boolean remove(String license) {
    int listsize = person.size(); // size before removing any
    for(int i=0; i<person.size(); i++) {
        if (person.get(i).getLicenseNumber().equals(license))
            person.remove(i--); // i-- is required because the list size will change if we remove from it, so we need to decrement i
    }

    return !(listsize == person.size()); // if the size before is equal to the size now, we never removed any and thus return false
}

如果您想要更简单的解决方案，可以查看method removeAll from ArrayList class