常见问题:如何使用自定义类的不同比较器对PriorityQueue中的对象进行排序?在Java中使用PriorityQueue与任何比较器
我试过用在适当的对与预期类似的排序结果在接下来的代码中的对象的priorityqueues和列表的这个比较要做到:
class User{
private Integer id;
private String name;
public User(Integer i, String n){
this.id=i;
this.name=n;
}
public Integer getId() {return id;}
public String getName() {return name;}
@Override
public boolean equals(Object obj) {
if (this == obj)return true;
if (obj == null)return false;
if (getClass() != obj.getClass())return false;
User other = (User) obj;
if(id == null){
if (other.id != null)return false;
}else if(!id.equals(other.id))return false;
return true;
}
@Override
public String toString() {return "[id:" + id + ", name:" + name + "]";}
}
public class MyPriorityQueue {
public static Comparator<User> cmpId = Comparator.comparingInt(x -> x.getId());
public static Comparator<User> cmpNameLength = Comparator.comparingInt(x -> x.getName().length());
public static void main(String[] args) {
List<User> users = new ArrayList<User>(10);
users.add(new User(1,"11111"));
users.add(new User(3,"333"));
users.add(new User(5,"5"));
users.add(new User(4,"44"));
users.add(new User(2,"2222"));
Queue<User> ids = new PriorityQueue<User>(10, cmpId); //use first comparator
users.forEach(x-> ids.offer(x));
Queue<User> names = new PriorityQueue<User>(10, cmpNameLength); //use second comparator
names.addAll(users);
System.out.println("Variant_1.1:");
ids.forEach(System.out::println);
System.out.println("Variant_2.1:");
names.forEach(System.out::println);
System.out.println("Variant_1.2:");
users.sort(cmpId); //use first comparator
users.forEach(System.out::println);
System.out.println("Variant_2.2:");
users.sort(cmpNameLength); //use second comparator
users.forEach(System.out::println);
}
}
输出:
Variant_1.1: //Failed sorted queue by user.id with using comporator cmpId
[id:1, name:11111]
[id:2, name:2222]
[id:5, name:5]
[id:4, name:44]
[id:3, name:333]
Variant_2.1: //Failed sorted queue by length of the user.name with cmpNameLength
[id:5, name:5]
[id:4, name:44]
[id:3, name:333]
[id:1, name:11111]
[id:2, name:2222]
Variant_1.2: // OK: correctly sorted list by user.id with cmpId comporator
[id:1, name:11111]
[id:2, name:2222]
[id:3, name:333]
[id:4, name:44]
[id:5, name:5]
Variant_2.2: //OK: for list by length of the user.name with cmpNameLength
[id:5, name:5]
[id:4, name:44]
[id:3, name:333]
[id:2, name:2222]
[id:1, name:11111]
我的预期即:
- 变体1.1和2.1的结果;
- 变体1.2和2.2的结果;
将是相同的,但它们是不同的。
我的问题:我为排序priorytyqueue /比较器做了什么错误,以及如何获得排序结果的优先队列作为我的例子中的适当列表?
感谢您澄清有关“的forEach”。纠正代码后“while(!ids.isEmpty())System.out.println(ids.poll());”而不是“ids.forEach(System.out :: println);”,获得了预期的结果。 –