Java 正在尝试从Arraylist中删除对象-仍然可以访问对象
我正在尝试添加从数组列表中删除对象的函数(首先,我想为这些对象生成唯一的随机ID:Java 正在尝试从Arraylist中删除对象-仍然可以访问对象,java,arraylist,Java,Arraylist,我正在尝试添加从数组列表中删除对象的函数(首先,我想为这些对象生成唯一的随机ID: import java.util.ArrayList; import java.util.ListIterator; import java.util.Random; public class Medium { public Medium(){ this.id = generateID(); System.out.println("ID: " + id);
import java.util.ArrayList;
import java.util.ListIterator;
import java.util.Random;
public class Medium {
public Medium(){
this.id = generateID();
System.out.println("ID: " + id);
mlist.add(this);
}
protected int generateID() {
Random random = new Random();
int id;
do {
id = 100 + (random.nextInt(999-100));
} while(idlist.contains(id));
idlist.add(id);
return id;
}
protected boolean delete(Medium delElem) {
boolean isDeleted = false;
ListIterator<Medium> it = mlist.listIterator();
while(it.hasNext()) {
it = mlist.listIterator();
Medium next = it.next();
if(delElem.getID() == next.getID()) {
delElem = next;
mlist.remove(delElem);
delElem = null;
if(delElem == null) {
System.out.println("Succesfull deleted");
}
isDeleted = true;
break;
}
}
return isDeleted;
}
protected int getID() {
return id;
}
public String getTitle() {
return title;
}
protected ArrayList<Medium> mlist = new ArrayList<Medium>();
private ArrayList<Integer> idlist = new ArrayList<Integer>();
protected String title;
protected final int id;
}
import java.util.ArrayList;
导入java.util.ListIterator;
导入java.util.Random;
公共类媒体{
公共媒体(){
this.id=generateID();
System.out.println(“ID:+ID”);
添加(本);
}
受保护的int-generateID(){
随机=新随机();
int-id;
做{
id=100+(random.nextInt(999-100));
}while(idlist.contains(id));
idlist.add(id);
返回id;
}
受保护的布尔删除(中等删除){
布尔值isDeleted=false;
ListIterator it=mlist.ListIterator();
while(it.hasNext()){
it=mlist.listIterator();
Medium next=it.next();
if(delElem.getID()==next.getID()){
delElem=next;
mlist.remove(delElem);
delElem=null;
if(delElem==null){
System.out.println(“成功删除”);
}
isDeleted=真;
打破
}
}
返回被删除;
}
受保护的int getID(){
返回id;
}
公共字符串getTitle(){
返回标题;
}
受保护的ArrayList mlist=新的ArrayList();
private ArrayList idlist=new ArrayList();
受保护的字符串标题;
受保护的最终int id;
}
我不确定我是否正确理解了这一点,但是如果我将delElem设置为满足相等id的对象,删除我的对象并将其设置为null,那么该对象就不应该再引用了。但是如果我在我的主函数中测试它,例如book.getTitle(),标题将被打印。我想这是因为它只是我函数中的一个局部对象。如果成功删除了对象,我如何全局删除函数中的对象并返回布尔值
谢谢!评论中已经说明,您通常不会手动删除对象(通过将对象设置为null)。当不再需要对象时,垃圾收集将完成它的工作 代码中奇怪的一点是,媒体将自己添加到列表中。为什么不创建另一个表示书架的类。通过这种方式,可以在书架上实现添加或删除书籍的方法:
package com.example;
import java.util.ArrayList;
import java.util.Random;
public class BookShelf {
protected ArrayList<Medium> mlist = new ArrayList<Medium>();
private ArrayList<Integer> idlist = new ArrayList<Integer>();
private class Medium {
protected int id;
protected String title;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
}
public Medium addMedium(String title) {
Medium medium = new Medium();
medium.setId(this.generateID());
medium.setTitle(title);
this.mlist.add(medium);
return medium;
}
protected int generateID() {
Random random = new Random();
int id;
do {
id = 100 + (random.nextInt(999 - 100));
} while (idlist.contains(id));
idlist.add(id);
return id;
}
protected boolean delete(Medium delElem) {
boolean isDeleted = false;
for (Medium medium : mlist) {
if (medium.getId() == delElem.getId()) {
mlist.remove(medium);
isDeleted = true;
break;
}
}
return isDeleted;
}
public ArrayList<Medium> getAllBooks() {
return this.mlist;
}
@Override
public String toString() {
StringBuilder strBuilder = new StringBuilder();
strBuilder.append("Books in the shelf: " + this.getAllBooks().size() + "\n");
for(Medium medium : this.getAllBooks()) {
strBuilder.append("Title: " + medium.getTitle() + "\n");
}
return strBuilder.toString();
}
public static void main(String[] args) {
BookShelf bookShelf = new BookShelf();
//Add two books to the shelf
Medium medium1 = bookShelf.addMedium("Book 1");
Medium medium2 = bookShelf.addMedium("Book 2");
System.out.println(bookShelf.toString());
//Delete one
bookShelf.delete(medium1);
System.out.println(bookShelf.toString());
}
}
package.com.example;
导入java.util.ArrayList;
导入java.util.Random;
公共类书架{
受保护的ArrayList mlist=新的ArrayList();
private ArrayList idlist=new ArrayList();
私人类媒体{
受保护的int-id;
受保护的字符串标题;
公共int getId(){
返回id;
}
公共无效集合id(内部id){
this.id=id;
}
公共字符串getTitle(){
返回标题;
}
公共无效集合标题(字符串标题){
this.title=标题;
}
}
公共媒体addMedium(字符串标题){
介质=新介质();
medium.setId(this.generateID());
中等。片名(片名);
此.mlist.add(中);
返回介质;
}
受保护的int-generateID(){
随机=新随机();
int-id;
做{
id=100+(random.nextInt(999-100));
}while(idlist.contains(id));
idlist.add(id);
返回id;
}
受保护的布尔删除(中等删除){
布尔值isDeleted=false;
用于(中等:mlist){
if(medium.getId()==delElem.getId()){
mlist.remove(中等);
isDeleted=真;
打破
}
}
返回被删除;
}
公共阵列列表getAllBooks(){
返回此.mlist;
}
@凌驾
公共字符串toString(){
StringBuilder strBuilder=新StringBuilder();
strBuilder.append(“书架上的书:“+this.getAllBooks().size()+”\n”);
for(中等:this.getAllBooks()){
strBuilder.append(“标题:+medium.getTitle()+”\n”);
}
返回strBuilder.toString();
}
公共静态void main(字符串[]args){
BookShelf BookShelf=新书架();
//在书架上加两本书
Medium medium1=书架添加Medium(“第1册”);
Medium medium2=书架添加Medium(“第二册”);
System.out.println(bookShelf.toString());
//删除一个
书架.删除(中1);
System.out.println(bookShelf.toString());
}
}
我认为我们需要更多的上下文,你从哪里获得了mlist
?比把所有的代码放在这里更好的是用额外的信息编辑你的文章。这有什么关系?一旦没有引用,它就有资格成为GC。如果目标是将它从发送的列表中删除,就像你已经完成了一样。我同意Dave。明确地说,d删除对象是Java中通常不做的事情。删除不再属于它们的引用,一旦对象不再被引用,它就有资格进行垃圾收集,并且可能会从内存中消失,谁在乎呢。但是,既然你显然在主方法中保留了引用,那就不会发生了。嗯,好吧如果我从列表中删除该对象并将其声明为null,则属性不应仍然可访问。但我明白,以这种方式,这不可能在全局范围内实现。非常感谢!