Java中按多个字段排序的最有效方法

Question

I'm working on a project where I have a table in memory, for example:

field1    field2    field3    field4    field5
somevalue somevalue somevalue somevalue somevalue
somevalue somevalue somevalue somevalue somevalue
    .
    . 
    .
    .
    v

What is the best way to write a function that would allow a user to specify some non-predetermined permutation of fields by which to sort? (ex./ sort by field2, then field1, then field5). The best method I thought of so far is a recursive function, but it gets ugly pretty quick, especially with creating and managing 'subgroups' of rows within each column. Can somebody point me in a more efficient direction before I commit to this convoluted approach?

By the way, my table is stored as a list of arrays.

Answer 1

The key thing to realize here is that your search algorithm always stays exactly the same. The only thing that changes is your actual comparison function.

I would recommend using a standard sort in the Arrays or Collections class, but writing your own custom Comparable class or Comparator , whose compare method will use the data the user supplies. This is actually kind of interesting - I've only ever written Comparable classes that use fixed data, but this is exactly a use case for them.

All you need to do is write the function

public int compare(Row row1, Row row2) {
    // iterate over the columns *in order of the user-supplied priority*
    // return appropriately
}

Here's documentation on the Comparable class .

And Comparator .

Which one you need depends on what you're implementing, I forget the details but should be straightforward.

The key #2 thing here is that you can instantiate your ColumnPrioritiesComparable class before the priorities are set. eg

class ColPriComp implements Comparable<ColPriComp> {
    private volatile int[] priorities; // possibly static, or obtained some other way,
    // so there's only one shared among all classes

    @Override
    public int compareTo(ColPriComp other) {
        // use "priorities" to do the comparison
    }

    public void setPriorities(int[] newPriorities) {
        this.priorities = newPriorities;
    }
}