在列表中查找某些属性具有相等值的对象

Question

给定一个对象列表(所有相同的类型),我如何确保它只包含某个属性的每个值的一个元素,即使equals()可能因为检查更多属性而为这些元素返回false？在代码中:

private void example() {
    List<SomeType> listWithDuplicates = new ArrayList<SomeType>();

    /*
     * create the "duplicate" objects. Note that both attributes passed to 
     * the constructor are used in equals(), though for the purpose of this 
     * question they are considered equal if the first argument was equal
     */
    SomeType someObject1 = new SomeObject1("hello", "1");
    SomeType someObject2 = new SomeObject1("hello", "2");

    List<SomeType> listWithoutDuplicates = removeDuplicates(listWithDuplicates)
    //listWithoutDuplicates should not contain someObject2
}

private List<SomeType> removeDuplicates(List<SomeType> listWithDuplicates) {
    /*
     * remove all but the first entry in the list where the first constructor-
     * arg was the same
     */
}

Answer 1

可以使用Set作为中间占位符来查找Bozho建议的重复项.这是一个示例removeDuplicates()实现.

private List<SomeType> removeDuplicates(List<SomeType> listWithDuplicates) {
    /* Set of all attributes seen so far */
    Set<AttributeType> attributes = new HashSet<AttributeType>();
    /* All confirmed duplicates go in here */
    List duplicates = new ArrayList<SomeType>();

    for(SomeType x : listWithDuplicates) {
        if(attributes.contains(x.firstAttribute())) {
            duplicates.add(x);
        }
        attributes.add(x.firstAttribute());
    }
    /* Clean list without any dups */
    return listWithDuplicates.removeAll(duplicates);
}