实现具有特定条件的比较器

Question

我需要实现 Comparator 以根据特定条件对 Employee 对象进行排序。

 class Employee
 {
      int employeeId;
      String employeeName;

 }

所以我手里已经有一个 List 的排序列表，我将排序顺序修改如下

1. 保持排序顺序
2. 如果 Employee 对象中的employeeName 是“Rock Hudson”，请将其添加到列表顶部。

>输入：

1 艾伦边境

2 贝蒂·爱德华兹

3 洛克哈德森

4 昆汀·塔伦蒂诺

5 伍迪艾伦

>输出：

3 洛克哈德森

1 艾伦边境

2 贝蒂·爱德华兹

4 昆汀·塔伦蒂诺

5 伍迪艾伦

Answer 1

你可以这样做

public static class Employee {
  // a constructor
  public Employee(int id, String name) {
    this.employeeId = id;
    this.employeeName = name;
  }

  // should be private and use getters and setters.
  int employeeId;
  String employeeName;

  // A special Comparator
  public static Comparator<Employee> rockHudsonComparator = new Comparator<Employee>() {
    @Override
    public int compare(Employee a, Employee b) {
      if (a.employeeName.equals("Rock Hudson")) {
        if (b.employeeName.equals("Rock Hudson")) {
          return 0;
        }
        return -1;
      } else if (b.employeeName.equals("Rock Hudson")) {
        return 1;
      }
      return a.employeeName
          .compareTo(b.employeeName);
    }
  };

  public String toString() {
    return "" + employeeId + " " + employeeName;
  }
}

public static void main(String[] args) {
  java.util.List<Employee> al = new java.util.ArrayList<Employee>();
  al.add(new Employee(1, "Alan Border"));
  al.add(new Employee(2, "Betty Edwards"));
  al.add(new Employee(3, "Rock Hudson"));
  al.add(new Employee(4, "Quentin Tarantino"));
  al.add(new Employee(5, "Woody Allen"));
  al.add(new Employee(6, "Rock Hudson")); // check the sort is stable.
  System.out.println("Before sort");
  System.out.println(al);
  java.util.Collections.sort(al,
      Employee.rockHudsonComparator);
  System.out.println("After sort");
  System.out.println(al);
}

哪些输出

[1 Alan Border, 2 Betty Edwards, 3 Rock Hudson, 4 Quentin Tarantino, 5 Woody Allen, 6 Rock Hudson]
[3 Rock Hudson, 6 Rock Hudson, 1 Alan Border, 2 Betty Edwards, 4 Quentin Tarantino, 5 Woody Allen]

Answer 2

public class MyEmployeeComparator implements Comparator<Employee> {

    private final String alwaysTopEmployee;

    public MyEmployeeComparator(final String alwaysTopEmployee) {
        this.alwaysTopEmployee = alwaysTopEmployee;
    }

    @Override
    public int compare(Employee o1, Employee o2) {
        if (o2.getName().equals(alwaysTopEmployee) && o1.getName().equals(alwaysTopEmployee))
            return 0;
        if (o1.getName().equals(alwaysTopEmployee))
            return -1;
        if (o2.getName().equals(alwaysTopEmployee))
            return 1;

        return o1.getName().compareTo(o2.getName());
    }
}

然后调用：

Collections.sort(stuff, new MyEmployeeComparator("Rock Hudson"));

Answer 3

针对这种情况，只需在每个方向上测试一个特殊条件：

Comparator<Employee> c = new Comparator<Employee>() {
    public int compare(Employee a, Employer b) {
        if (a.getName().equals("Rock Hudson"))
             return -1;
        if (b.getName().equals("Rock Hudson"))
             return 1;
        return a.getName().compareTo(b.getName());
    }
}