Java CookBook--Creating a Priority Queue--by Tim O'Brien 整理by博主

  按优先级排列的集合对象PriorityBuffer用法，来自org.apache.commons.collections.buffers.PriorityBuffer

  PriorityBuffer使用比较器Comparator来排列内容，若使用不包含比较器Comparator的PriorityBuffer，此时所有放入PriorityBuffer中的对象都要实现Comparable接口，PriorityBuffer会使对象按照自然顺序排列。

  如下，不包含比较器Comparator的PriorityBuffer的使用实例：

  

import java.util.Iterator;
import org.apache.commons.collections.Buffer;
import org.apache.commons.collections.buffer.PriorityBuffer;

public class BufferTest {
	public static void main(String[] args) {
		/**
		 * a PriorityBuffer uses the Comparator to sort its contens,returning the element of 
		 * greatest priority.Using a PriorityBuffer without a Comparator causes the buffer to
		 * prioritize objects by natural order,casting each object to Comparable and comparing 
		 * objects with CompareTo() method;all objects must implement the Comparable interface
		 * if no Comparator is supplied.
		 */
		Buffer priority=new PriorityBuffer();
		priority.add(new Long(2));
		priority.add(new Long(1));
		priority.add( new Long( 20 ) );
		priority.add( new Long( 7 ) );
		priority.add( new Long( 18 ) );
		priority.add( new Long( 1 ) );
		// Print the results in priority order
		Iterator priorityIterator = priority.iterator( );
		while( priorityIterator.hasNext( ) ) {
		Long value = (Long) priorityIterator.next();
		System.out.println( "Value: " + value );
		}
	}
}

输出结果如下

Value: 1
Value: 2
Value: 1
Value: 7
Value: 18
Value: 20

    PriorityBuffer就像Buffer的实现一样，定义了那个对象被优先remove的机制，接下来说说包含比较器的PriorityBuffer。以急症室举例，一般病人的医治顺序与病人病情的严重程度与病人等待时间相关，严重的有生命危险的病人比一般性病人在看病的顺序上有优先权，假设你有一个Patient病人实例，有name,severity和checkIn属性。病人的严重度severity是从0到10的数字，0最低，10最严重。病人进入候诊室的时间checkIn是在相同严重度下决定优先级的要素。

  如下：病人对象

import java.util.Date;

public class Patient {
	private String name;
	private Integer severity;
	private Date checkIn;
	public Patient(){

	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Integer getSeverity() {
		return severity;
	}
	public void setSeverity(Integer severity) {
		this.severity = severity;
	}
	public Date getCheckIn() {
		return checkIn;
	}
	public void setCheckIn(Date checkIn) {
		this.checkIn = checkIn;
	}

}

  根据病人的情况判断就诊次序的比较器对象如下，实现了Comparator接口：

import java.util.Comparator;

public class PatientPriorityComparator implements Comparator {

	@Override
	public int compare(Object o1, Object o2) {
		int comparison = -1;
		if( o1 instanceof Patient &&
				o2 instanceof Patient ) {
			Patient p1 = (Patient) o1;
			Patient p2 = (Patient) o2;
			comparison = p2.getSeverity( ).compareTo( p1.getSeverity( ) );
			if( comparison == 0 ) {
				comparison =
						p2.getCheckIn( ).compareTo( p1.getCheckIn( ) );
			}
		}
		return comparison;
	}
  
}

候诊室的实现：

import java.util.Date;
import org.apache.commons.collections.Buffer;
import org.apache.commons.collections.buffer.PriorityBuffer;

public class WaitingRoomApp {
	public static void main(String[] args) {
		WaitingRoomApp example = new WaitingRoomApp( );
		example.start( );
		}
	public void start(){
		Buffer patients =
				new PriorityBuffer( new PatientPriorityComparator( ) );
		Patient johnDoe1 = new Patient( );
		johnDoe1.setName( "John Doe 1" );
		johnDoe1.setSeverity( new Integer( 7 ) );
		johnDoe1.setCheckIn( new Date( ) );
		patients.add( johnDoe1 );
		Patient johnDoe2 = new Patient( );
		johnDoe2.setName( "John Doe 2" );
		johnDoe2.setSeverity( new Integer( 9 ) );
		johnDoe2.setCheckIn( new Date( ) );
		patients.add( johnDoe2 );
		Patient janeDoe3 = new Patient( );
		janeDoe3.setName( "Jane Doe 3" );
		janeDoe3.setSeverity( new Integer( 9 ) );
		janeDoe3.setCheckIn( new Date( ) );
		patients.add( janeDoe3 );
		while( patients.size( ) > 0 ) {
			Patient patient = (Patient) patients.remove( );
			System.out.println( "Patient: " + patient.getName( ) );
		}


	}
}

结果如下：

Patient: John Doe 2
Patient: Jane Doe 3
Patient: John Doe 1