java - 比较方法违反了排序方法中的一般契约

Question

我的排序方法出现错误。

Comparison method violates its general contract

这是我使用排序方法的排序对象

public abstract class ComparablePerson extends IDValueItem implements
        Comparable<ComparablePerson> {

    private int score;
    private String itemID,itemName;

    //setters and getters

    public int compareTo(ComparablePerson another) {
    if (score == another.getScore())
        return this.getItemName().compareToIgnoreCase(another.getItemName());
    else if ((score) > another.getScore())
        return 1;
    else
        return -1;
}

@Override
public boolean equals(Object o) {
    final ComparablePerson other = (ComparablePerson) o; 

    if (score == other.getScore() && this.getItemName().equalsIgnoreCase(other.getItemName())) 
        return true; 
    else 
        return false; 
}

我只是打电话 Collections.sort(ComparablePersonCollection);

这可能是什么原因造成的？

Answer 1

compareTo和equals方法实现似乎不一致，错误告诉您对于相同的两个对象 equals给出 true while compareTo不产生零，这是不正确的。我建议您调用compareTo来自equals确保一致性或以其他方式定义自定义 Comparator<T> .

简单地做:

public abstract class ComparablePerson extends IDValueItem implements Comparable<ComparablePerson> {

    private int score;
    private String itemID,itemName;

    //setters and getters

    public int compareTo(ComparablePerson another) {
    if (score == another.getScore())
        return this.getItemName().compareToIgnoreCase(another.getItemName());
    else if ((score) > another.getScore())
        return 1;
    else
        return -1;
    }

    @Override
    public boolean equals(Object o) {
        return compareTo(o) == 0; 
    }   
}