错误：（19、21）java：不兼容的类型：java.lang.Object 无法转换为项目

Question

I'm writing a program using Jaxb to convert an xml file into a java object. However, in my main class, I'm extending my item class to my items class to get access to the data stored in there, but it's telling me that it requires an object and it received an item instead. I'm a bit confused. When I build the file I get the error message in the title.

Here's my main class-- I'm getting the error in the for loop for item

import java.io.*;
import java.util.List;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

public class main {
    public static void main(String[] args) throws IOException, JAXBException {
        File file = new File("items.xml");

        JAXBContext context = JAXBContext.newInstance(items.class);
        Unmarshaller un = context.createUnmarshaller();
        items itemData = (items) un.unmarshal(file);

        List items = itemData.getitem();

        for(item e: items){
            System.out.println("DataType : "+e.getDataType());
            System.out.println("Name : "+e.getName());
            System.out.println("Data : "+e.getData());
            System.out.println("Group : "+e.getGroup());
            System.out.println("--------------------------");
        }
    }
}

Here's my item class

import javax.xml.bind.annotation.XmlElement;

public class item {
    private String dataType;
    private String name;
    private int data;
    private String group;

    @XmlElement
    public String getDataType(){
        return dataType;
    }
    public void setDataType(String dataType){
        this.dataType = dataType;
    }

    @XmlElement
    public String getName(){
        return name;
    }
    public void setName(String name){
        this.name = name;
    }

    @XmlElement
    public int getData(){
        return data;
    }
    public void setData(int data){
        this.data = data;
    }

    @XmlElement
    public String getGroup(){
        return group;
    }
    public void setGroup(String group){
        this.group = group;
    }
}

Here is my items class

import java.util.List;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement(name = "items")
public class items {
    private List<item> item;

    @XmlElement(name = "item")
    public List<item> getItem(){
        return item;
    }

    public void setItem(List<item> itemList){
        this.item = itemList;
    }
}

Here is my xml file

<items> 
      <item>
            <dataType>Number</dataType>
            <name>Harry Potter 1</name>
            <data>5</data>
            <group>Movie</group>
      </item>
      <item>
            <dataType>Number</dataType>
            <name>Harry Potter 2</name>
            <data>6</data>
            <group>Movies</group>
            <items>
                  <item>
                        <dataType>Number</dataType>
                        <name>Harry Potter 3</name>
                        <data>7</data>
                        <group>Books</group>
                  </item>
                  <item>
                        <dataType>Number</dataType>
                        <name>Harry Potter 4</name>
                        <data>8</data>
                        <group>Books</group>
                  </item>
            </items>
      </item>
</items>

Answer 1

change

List items = itemData.gettem();

to

List<item> items = itemData.getItem();

Answer 2

Firstly, as answered by Anique Azhar, fix your compilation error from

List items = itemData.getitem();

to

List<item> items = itemData.getItem();

Secondly, as said by Abra in the question comment, The class name should be Capitalized.

Then to handle the element <items> nested in <item> , add a field items of class Items to class Item .

public class Item {
    private String dataType;
    private String name;
    private int data;
    private String group;
    private Items items;
    
    // getter and setter
}

My working code is available in Github . See the commit history for what I did based on your code.

Your programming journey is long. Keep on. Take some time to learn Git . Next time ask question on stackoverflow, better share your code in Github. It make people locate the problem faster.