我正在寻找一种在java中存储一组数字的方法
当我生成一个新号码时，我必须查看该号码中是否存在该号码。
我使用了这样声明的Hashset：
HashSet<Integer> tempSet;
tempSet = new HashSet<Integer>();
但是当我这样测试时它不起作用：
int randomNumber = rand.nextInt(10);
while (tempSet.contains(randomNumber))
{
randomNumber = rand.nextInt(10);
System.out.println("randomNumber= " + randomNumber );
}
这意味着如果在集合中生成并存在已编号，则使用HashSet的contains成员函数的测试不起作用
这是完整的代码：
package ex1;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Random;
public class Main {
public static void main(String[] args) {
//1- create 10 courses
Course[] courseLists = new Course[10];
for(int i=0; i<10; i++){
//create
Course course = new Course("course"+i, "courseId"+i, "", 60.0f, 0, 0.0f);
courseLists[i]=course;
}
//2- create 7 professors
Professor[] professorLists = new Professor[7];
Random rand= new Random();
int min=1;
int max = 6;
for(int i=0; i<7; i++){
//create
Professor professor = new Professor
(
"ProfessorFirstName"+i, "ProfessorLastName"+i,
35, "MALE", "adress"+i, "professorId"+i
);
courseLists[i].setAssignedProfessor("profId"+i);
professor.setCourseList(courseLists[i]);
professorLists[i] = professor;
}
rand= new Random();
int randomNum1 = rand.nextInt((max - min) + 1) + min;
int randomNum2 = rand.nextInt((max - min) + 1) + min;
while ( randomNum2 == randomNum1 ) {
randomNum2 = rand.nextInt((max - min) + 1) + min;
}
courseLists[8].setAssignedProfessor("profId"+randomNum1);
professorLists[randomNum1].setCourseList(courseLists[8]);
courseLists[9].setAssignedProfessor("profId"+randomNum2);
professorLists[randomNum2].setCourseList(courseLists[9]);
courseLists[7].setAssignedProfessor("profId"+1);
professorLists[1].setCourseList(courseLists[7]);
//3- create 30 students
Student[] studentsLists = new Student[30];
//--------------------
boolean genderValue;
//generate number of courses per student
//randomNbrCourses: number of courses taken by the current student
for(int i=0; i<30; i++){
int minNbrCourses = 1;
int maxNbrCourses = 6;
int randomNbrCourses;
rand= new Random();
randomNbrCourses = rand.nextInt
(
(maxNbrCourses - minNbrCourses) + 1
) + minNbrCourses;
//generate random age
int minStudentAge=18;
int maxStudentAge = 48;
int randomAge = -1;
rand= new Random();
randomAge = rand.nextInt
(
(maxStudentAge - minStudentAge) + 1
) + minStudentAge;
//gender
genderValue = Math.random() < 0.5;
String gender;
if (genderValue == false)
gender = "FEMALE";
else
gender = "MALE";
//****************************Here I have the HashSet *********//
HashSet<Integer> tempSet;
tempSet = new HashSet<Integer>();
//****************************************************************//
GradeBook gradeBook = new GradeBook();
for ( int nbrCourse=0; nbrCourse<randomNbrCourses; nbrCourse++) {
Tuple tupleValue = new Tuple();
//generate one number , this number correspand to a course id...
//** Here I have to test if a new number exist in the set or not **//
int randomNumber = rand.nextInt(10);
while (tempSet.contains(randomNumber))
{
randomNumber = rand.nextInt(10);
System.out.println("randomNumber= " + randomNumber );
}
//*************************************************//
courseLists[randomNumber].setNbrEnrolledStudent(1);
float minMark=0.0f;
float maxMark=100.0f;
Random newRand= new Random();
//generate four random marks for the course....
float randomMark1 = newRand.nextFloat()*(100.0f-0.0f) + 0.0f;
tupleValue.setMarkExam1(randomMark1);
float randomMark2 = newRand.nextFloat()*(100.0f-0.0f) + 0.0f;
tupleValue.setMarkExam2(randomMark2);
float randomMark3 = newRand.nextFloat()*(100.0f-0.0f) + 0.0f;
tupleValue.setMarkExam3(randomMark3);
float randomMark4 = newRand.nextFloat()*(100.0f-0.0f) + 0.0f;
tupleValue.setMarkExam4(randomMark4);
tupleValue.setFinalMark
(
(randomMark1+randomMark2+randomMark3+randomMark4)/4
);
tupleValue.setCourseName("course"+randomNumber);
tupleValue.setCourseId("courseId"+randomNumber);
gradeBook.setCourseLists(tupleValue);
}
Student student = new Student
(
"firstName_student"+i,"lastName_student"+i,
randomAge, gender, "adress"+i, "idStudent"+i, gradeBook
);
studentsLists[i]=student;
studentsLists[i].setNbrCourses(randomNbrCourses);
}
//we have to verify that there is no course with less than 3 student enrolled
//print the list of courses
getWholeCouces(courseLists, studentsLists);
//print the professors and there assigned courses
getProfessorsAndAssignedCouces(professorLists);
//print the list of all students and the courses enrolled in
getStudentsWithEnrolledCourses(studentsLists);
}
/*
static float getMinMarkCourse(){
}
static float getMaxMarkCourse(){
}
static float getGroupMarkCourse(){
}*/
//method to print the list of all students and the courses they are enrolled in
static void getStudentsWithEnrolledCourses(Student[] student){
System.out.println(" ");
System.out.println("----------------------------------------------------------");
System.out.println("list of all students and the courses they are enrolled in:");
System.out.println("----------------------------------------------------------");
for (int i=0; i<30;i++){
System.out.print(student[i].getLastName());
System.out.print(" "+student[i].getIdentificationNumber());
GradeBook gb = student[i].getGradeBook();
ArrayList<Tuple> tuple = gb.getCourseLists();
for (int L=0; L< tuple.size(); L++)
{
System.out.println(" ");
System.out.print(" "+tuple.get(L).getCourseId());
System.out.print(" "+tuple.get(L).getFinalMark());
}
System.out.println(" ");
System.out.println(" ");
}
}
//method to get the professors and there assigned courses
static void getProfessorsAndAssignedCouces(Professor[] professor){
System.out.println(" ");
System.out.println("---------------------------------------");
System.out.println("professors and there assigned courses:");
System.out.println("---------------------------------------");
for(int i=0; i<7; i++){
System.out.println(" ");
System.out.print(professor[i].getFirstName());
System.out.print(" "+professor[i].getIdentificationNumber());
System.out.println(" ");
System.out.println(" ");
List<Course> courseList = professor[i].getCourseList();
for (int k=0; k < courseList.size(); k++){
System.out.print(" "+courseList.get(k).getCourseId());
System.out.print(" "+courseList.get(k).getNbrEnrolledStudent());
System.out.print(" "+courseList.get(k).getAverageCourseMark());
System.out.println(" ");
}
System.out.println(" ");
}
}
//method to get the list of all courses
static void getWholeCouces(Course[] courseList,Student[] studentsList){
System.out.println("----------------");
System.out.println("list of courses:");
System.out.println("----------------");
// maxMark = max mark of the course
// minMark = minimum mark of the course
float maxMark = Float.MIN_VALUE;
float minMark = Float.MAX_VALUE;
float allMarks = 0.0f;
float nbOfEnrolledStudent=0.0f;
for(int i=0; i<10; i++){
//create
String courseName = courseList[i].getCourseName();
//look for enrolled student
for(int nbStudent=0; nbStudent<30; nbStudent++){
ArrayList<Tuple> temp =
studentsList[nbStudent].getGradeBook().getCourseLists();
for (int j=0;j< temp.size();j++){
if (temp.get(j).getCourseName().equals(courseName)){
if (temp.get(j).getFinalMark() > maxMark )
maxMark = temp.get(j).getFinalMark();
if (temp.get(j).getFinalMark() < minMark )
minMark = temp.get(j).getFinalMark();
allMarks += temp.get(j).getFinalMark();
nbOfEnrolledStudent+=1;
}
}
}
courseList[i].setAverageCourseMark((allMarks)/nbOfEnrolledStudent);
System.out.print(courseName);
System.out.print(" "+courseList[i].getCourseId());
System.out.print(" "+courseList[i].getAssignedProfessor());
System.out.print(" "+courseList[i].getNbrEnrolledStudent());
System.out.print(" "+minMark);
System.out.print(" "+maxMark);
System.out.print(" "+(allMarks)/nbOfEnrolledStudent);
System.out.println(" ");
}
}
}
答案 0 :(得分：5)
您没有向HashSet添加任何数字，因此当然contains总是返回false。
int randomNumber = rand.nextInt(10);
while (tempSet.contains(randomNumber))
{
randomNumber = rand.nextInt(10);
System.out.println("randomNumber= " + randomNumber );
}
tempSet.add(randomNumber); // add this
答案 1 :(得分：2)
此处无需使用contains方法。如果元素已经存在于其中，则add() set方法返回布尔值。
所以，我们可以这样做：
if(!tempSet.add(randomNumber)){
//do something as the number is already present
}
这将使我们免于编写else块，因为该元素已在if块中添加。
答案 2 :(得分：1)
利用收藏（集）......
如果插入失败，则执行mySet.add会返回false，并且设置不允许重复...
示例摘录：
Set<Integer> mySet = new HashSet<Integer>();
for (int i = 0; i < 12; i++) {
System.out.println(mySet.add(new Random().nextInt(4)));
}
System.out.println(mySet);
输出到此可以是：
true
true
false
false
true
false
true
false
false
false
false
false
[0, 1, 2, 3]