为什么会出现TreeSet.add 报空指针异常

[无痛学习]

在向TreeSet中add对象的时候，总是报空指针异常

import java.util.Comparator;
import java.util.Iterator;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;

import org.junit.Test;

/*
 * 练习 TreeSet的自然排序和定制排序
 */
public class TestTreeSet {
	@Test
	public void test() {
		//自然排序
		Set<Item> set = new TreeSet<Item>();
		set.add(new Item("Billy",4547));//此处报空指针异常
		set.add(new Item("Eric",3369));
		set.add(new Item("Magic",3608));
		for(Object obj:set){
			System.out.println(obj);
		}
		
		//定制排序
		Comparator<Item> com = new Comparator<Item>() {
			@Override
			public int compare(Item o1, Item o2) {

				Item it1 = (Item) o1;
				Item it2 = (Item) o2;
				int i = it1.getPartNum().compareTo(it2.getPartNum());
				if (i == 0) {
					return it1.getDescription().compareTo(it2.getDescription());
				} else {
					return i;
				}
			}

		};

		SortedSet<Item> parts = new TreeSet<Item>(com);
		parts.add(new Item("Tom", 1456));
		parts.add(new Item("Sam", 2580));
		parts.add(new Item("Kimi", 3369));
		parts.add(new Item("Penny", 1234));

		for (Object obj : parts) {
			System.out.println(obj);
		}
	}
}

Item类，实现Comparable接口，实现hashCode，equals，compareTo方法

public class Item implements Comparable {

	private String description;
	private Integer partNum;
	//构造器
	public Item(){
		
	}
	public Item(String description, Integer patrNum) {
		super();
		this.description = description;
		this.partNum = partNum;
	}

	public void setDescription(String description) {
		this.description = description;
	}

	public String getDescription() {
		return this.description;
	}

	public Integer getPartNum() {
		return partNum;
	}
	public void setPartNum(Integer partNum) {
		this.partNum = partNum;
	}

	@Override
	public String toString() {
		return "Item [description=" + description + ", partNum=" + partNum
				+ "]";
	}
	
	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result
				+ ((description == null) ? 0 : description.hashCode());
		result = prime * result + ((partNum == null) ? 0 : partNum.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Item other = (Item) obj;
		if (description == null) {
			if (other.description != null)
				return false;
		} else if (!description.equals(other.description))
			return false;
		if (partNum == null) {
			if (other.partNum != null)
				return false;
		} else if (!partNum.equals(other.partNum))
			return false;
		return true;
	}

	@Override
	public int compareTo(Object o) {
		if(o instanceof Item){
			Item it = (Item)o;
			int i = this.partNum.compareTo(it.partNum);
			if(i == 0){
				return this.description.compareTo(it.description);
			}else{
				return i;
			}
		}
		return 0;
	}

}

一直想不明白，初学java，请帮我看一下好吗

[zs808]

看一下详细的异常堆栈，注意栈顶（最上面那行）对应的方法

[无痛学习]

谢谢，我找到原因了，是构造器参数的问题。eclipse没有识别出这两个参数名是一样的，我也是醉了。 public Item(String description, Integer patrNum) { super(); this.description = description; this.partNum = partNum; } 怪不得每次声明对象的时候，Integer的值总是null，原来根本就没传进去

[galiniur0u]

    public Item(String description, Integer patrNum) {
        super();
        this.description = description;
        this.partNum = partNum;
    }

楼主，你变量敲错了哈， Integer patrNum