java并发和排序的简单例子(Runnable+TreeSet)
作者：互联网
很多时候并发需要考虑线程安全，但也有很多时候和线程安全毛关系都没有，因为并发最大的作用是并行，线程安全仅仅是并发的一个子话题。
例如常常会用于并发运算，并发i/o。
下文是一个练习笔记。
运行环境：windows 11,jdk17
1.Pojo--StudentExamScoreSummary
package study.model.school;
import java.math.BigDecimal;
import java.util.Date;
public class StudentExamScoreSummary implements Comparable<StudentExamScoreSummary>{
private Integer id;
private Integer studentId;
private Integer theYear;
private BigDecimal lanScore;
private BigDecimal mathScore;
private BigDecimal physicalScore;
private BigDecimal politicsScore;
private BigDecimal philosophyScore;
private BigDecimal avgScore;
private Date optime;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public Integer getStudentId() {
return studentId;
}
public void setStudentId(Integer studentId) {
this.studentId = studentId;
}
public Integer getTheYear() {
return theYear;
}
public void setTheYear(Integer theYear) {
this.theYear = theYear;
}
public BigDecimal getLanScore() {
return lanScore;
}
public void setLanScore(BigDecimal lanScore) {
this.lanScore = lanScore;
}
public BigDecimal getMathScore() {
return mathScore;
}
public void setMathScore(BigDecimal mathScore) {
this.mathScore = mathScore;
}
public BigDecimal getPhysicalScore() {
return physicalScore;
}
public void setPhysicalScore(BigDecimal physicalScore) {
this.physicalScore = physicalScore;
}
public BigDecimal getPoliticsScore() {
return politicsScore;
}
public void setPoliticsScore(BigDecimal politicsScore) {
this.politicsScore = politicsScore;
}
public BigDecimal getPhilosophyScore() {
return philosophyScore;
}
public void setPhilosophyScore(BigDecimal philosophyScore) {
this.philosophyScore = philosophyScore;
}
public BigDecimal getAvgScore() {
return avgScore;
}
public void setAvgScore(BigDecimal avgScore) {
this.avgScore = avgScore;
}
public Date getOptime() {
return optime;
}
public void setOptime(Date optime) {
this.optime = optime;
}
public BigDecimal calAvgScore() {
return (this.lanScore.add(this.mathScore).add(this.physicalScore).add(this.politicsScore)
.add(this.philosophyScore)).divide(new BigDecimal(5));
}
@Override
public int compareTo(StudentExamScoreSummary o) {
return this.avgScore.compareTo(o.getAvgScore());
}
}
2.线程和测试代码-ConcurrentListRunable
/**
*
*/
package study.base.types.collection.list;
import java.math.BigDecimal;
import java.math.RoundingMode;
import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.TreeSet;
import java.util.concurrent.ConcurrentHashMap;
import study.model.school.StudentExamScoreSummary;
/**
* @author luzhifei
*
*/
public class ConcurrentListRunable implements Runnable {
private List<StudentExamScoreSummary> scoreList;
DecimalFormat df = new DecimalFormat("#00.0");
ConcurrentHashMap<String, Boolean> flag;
public ConcurrentListRunable(List<StudentExamScoreSummary> list, ConcurrentHashMap<String, Boolean> flag) {
this.scoreList = list;
this.flag = flag;
}
@Override
public void run() {
int len = scoreList.size();
String courseName = Thread.currentThread().getName();
for (int i = 0; i < len; i++) {
StudentExamScoreSummary item = scoreList.get(i);
double rscore = Math.random() * 100;
BigDecimal dScore = new BigDecimal(rscore);
dScore.setScale(1, RoundingMode.HALF_UP);
synchronized (scoreList) {
switch (courseName) {
case "语文":
item.setLanScore(dScore);
break;
case "数学":
item.setMathScore(dScore);
break;
case "物理":
item.setPhysicalScore(dScore);
break;
case "政治":
item.setPoliticsScore(dScore);
break;
case "哲学":
item.setPhilosophyScore(dScore);
break;
}
}
//System.out.println(item.getId().toString() + "-[" + courseName + "]" + df.format(dScore));
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
synchronized (flag) {
flag.put(courseName, true);
}
}
public static void main(String[] args) {
int tty=10;
String[] courses = new String[] { "数学", "语文", "物理", "政治", "哲学" };
ConcurrentHashMap<String, Boolean> flag = new ConcurrentHashMap<String, Boolean>(5);
for (int i = 0; i < courses.length; i++) {
flag.put(courses[i], false);
}
List<StudentExamScoreSummary> sList = new ArrayList<StudentExamScoreSummary>();
for (int i = 0; i < tty; i++) {
StudentExamScoreSummary score = new StudentExamScoreSummary();
score.setId(i);
score.setStudentId(i);
score.setTheYear(2024);
sList.add(score);
}
List<StudentExamScoreSummary> conList = Collections.synchronizedList(sList);
ConcurrentListRunable job = new ConcurrentListRunable(conList, flag);
List<Thread> jobs = new ArrayList<>();
for (int i = 0; i < courses.length; i++) {
Thread t = new Thread(job, courses[i]);
jobs.add(t);
}
for (int i = 0; i < courses.length; i++) {
jobs.get(i).start();
}
boolean isDone = false;
while (isDone == false) {
isDone = true;
for (int i = 0; i < courses.length; i++) {
if (flag.get(courses[i]) == false) {
isDone = false;
break;
}
}
}
DecimalFormat df = new DecimalFormat("#00.0");
for (int i = 0; i < sList.size(); i++) {
StudentExamScoreSummary item = sList.get(i);
BigDecimal avgScore = item.calAvgScore();
item.setAvgScore(avgScore);
System.out.println(item.getStudentId().toString() + " 平均成绩:" + df.format(avgScore));
}
// 排序
System.out.println("排序------------------------------------------");
TreeSet<StudentExamScoreSummary> ts = new TreeSet<StudentExamScoreSummary>(sList);
for (Iterator<StudentExamScoreSummary> iter = ts.iterator(); iter.hasNext();) {
StudentExamScoreSummary item=iter.next();
System.out.println(item.getStudentId().toString() + " 平均成绩:" + df.format(item.getAvgScore()));
}
}
}
测试结果1：
0 平均成绩:48.8 1 平均成绩:53.7 2 平均成绩:43.8 3 平均成绩:56.9 4 平均成绩:64.9 5 平均成绩:49.9 6 平均成绩:51.0 7 平均成绩:58.4 8 平均成绩:61.3 9 平均成绩:48.5 排序------------------------------------------ 2 平均成绩:43.8 9 平均成绩:48.5 0 平均成绩:48.8 5 平均成绩:49.9 6 平均成绩:51.0 1 平均成绩:53.7 3 平均成绩:56.9 7 平均成绩:58.4 8 平均成绩:61.3 4 平均成绩:64.9
注意事项：
1.StudentExamScoreSummary必须实现Comparable接口，因为测试代码使用TreeSet
TreeSet<StudentExamScoreSummary> ts = new TreeSet<StudentExamScoreSummary>(sList);
以上代码调用的构造函数是：
public TreeSet(Collection<? extends E> c) {
this();
addAll(c);
}
这个构造函数要求入参必须实现Comparable接口（如果参数不是简单的java类型)。
2.ConcurrentHashMap和Collections.synchronizedList的结果要求手动调用sychronized
否则可能会线程不安全。
3.代码仅仅是为了演示使用5个线程各自生成成绩，不考虑效率问题。高效且正确的做法应该是分别计算5个不相干的List。
我们需要使用并发list的时候，正常情况下，多数是因为以下理由：
- 对list的操作仅仅占据了很少的计算资源，线程更多的时候是做其它更耗费资源的事情
- 为了实现异步操作
标签：Runnable,java,BigDecimal,item,new,成绩,public,TreeSet 来源： https://www.cnblogs.com/lzfhope/p/16328127.html