我需要编写一个方法，通过学生ID从ArrayList（myRoster）中删除学生。如果学生ID不存在，则该方法应打印一条错误消息，指出未找到该ID。我写了一个删除方法，我可以通过索引删除项目。错误消息“找不到ID 3的学生”返回6次（第一次删除3次，第二次错误消息3次）。但是我希望得到一个错误消息，我在main方法中调用第二个删除方法。一点帮助将不胜感激。
学生班级
public class Student {
private int StudentID;
private String FirstName;
private String LastName;
private String Email;
private int age;
private int[] Grades;
//Constructor
public Student(int S_ID,String fName,String lName,String email,int Age,
int[] grade){
setStudentID(S_ID);
setFirstName(fName);
setLastName(lName);
setEmail(email);
setAge(Age);
setGrade(grade);
}
//Accessor Methods (get methods)
public int getStudentID(){
return StudentID;
}
public String getFirstName(){
return FirstName;
}
public String getLastName(){
return LastName;
}
public String getEmail(){
return Email;
}
public int getAge(){
return age;
}
public int[] getGrades(){
return Grades;
}
//Mutator methods (set methods)
public void setStudentID(int StudentID){
this.StudentID=StudentID;
}
public void setFirstName(String FirstName){
this.FirstName=FirstName;
}
public void setLastName(String LastName){
this.LastName=LastName;
}
public void setEmail(String Email){
this.Email=Email;
}
public void setAge(int age){
this.age=age;
}
public void setGrade(int Grade[]){
this.Grades=Grade;
}
}
名册等级
import java.util.ArrayList;
public class Roster {
private static ArrayList<Student> myRoster= new ArrayList<>();
public static void main(String[] args) {
add(1,"John", "Smith", "John1989@gmail.com", 20, 88,79, 59);
add(2,"Suzan", "Erickson", "Erickson_1990@gmailcom",19,91,72,85);
add(3,"Jack","Napoli","The_lawyer99yahoo.com",19,85,84,87);
add(4,"Erin", "Black","Erin.black@comcast.net",22,91,98,82 );
add(5,"Henry","Adam","adam1@gmail.com",25,85,84,79);
remove(3);
remove(3);//expected: This should print a message saying such a student with this ID was not found
}
public static void add(int S_ID,String fName,String lName,String email,int
Age, int grade1, int grade2, int grade3){
int[] Grades={grade1, grade2,grade3};
Student newStudent= new Student(S_ID, fName, lName, email, Age, Grades);
myRoster.add(newStudent);
}
public static void remove(int StudentID){
for (int i = 0; i < myRoster.size(); i++){
if(i == StudentID){
myRoster.remove(i);
}else{
System.out.println("Student with ID "+StudentID+" was not found");
}
}
}
}
}
答案 0 :(得分：2)
i与参数StudentID进行比较，而应该是if(myRoster.get(i).getStudentID == StudentID)。为什么文本＆＃34; ID＆＃34; + StudentID +＆＃34;未找到＆＃34; 多次打印到控制台是因为您已将其插入循环内，这意味着每次参数StudentID与该值不匹配时它被比较，它将打印相同的消息...
要完成您的任务，您只需使用ArrayList#removeIf方法删除指定Student的{{1}}，否则如果ArrayList#removeIf返回false，则可以打印适当的消息，如下面的解决方案所示。
StudentID答案 1 :(得分：0)
你的问题似乎是你的remove（）方法中的循环不是在studentID上循环，而是循环索引。你应该遍历studentIDs。每次ID与给定ID不匹配时，您的代码都会打印出来。这就是您获得多条打印消息的原因。如果没有人匹配，你应该只打印（即名单大小不会改变）。
public static void remove(int StudentID){
int initialSize = myRoster.size(); //store initial size of roster to check if it changes
for (int i=0;i<myRoster.size();i++){
if(myRoster.get(i).getStudentID == StudentID){
myRoster.remove(i);
}
}
//checks if a student was removed which means the ID was found.
if(initialSize == myRoster.size()){
System.out.println("Student with ID "+StudentID+" was not found");
}
}
答案 2 :(得分：0)
您也可以使用 Iterator 界面，如下所示。
public static void remove(int StudentID) {
Iterator<Student> it = myRoster.iterator();
while(it.hasNext()) {
Student stud = (Student)it.next();
if (stud.getStudentID() == StudentID) {
it.remove();
return;
}
}
System.out.println("Student with ID " + StudentID + " was not found");
}
答案 3 :(得分：0)
您的删除方法目前为列表中没有所需学生ID的每个学生提供一次错误消息。
for (int i=0;i<myRoster.size();i++){
if(i==StudentID){
myRoster.remove(i);
}else{
System.out.println("Student with ID "+StudentID+" was not found"); }
只要索引i的学生没有所需的ID，就会调用该打印语句，而不是在没有学生拥有该ID的情况下。
解决此问题的一种简单方法是在方法的开头放置boolean并将其设置为false。然后，在if (i == StudentID)块中，删除学生并将值设置为true。然后，在循环完成后，检查布尔值是否为真;如果确实如此，那么所需的学生已被删除。如果它仍然是假的，则没有具有所需ID的学生。
看起来应该是这样的：
public static void remove(int studentID) {
boolean studentFound = false;
for (int i=0;i<myRoster.size();i++){
if(i==StudentID){
myRoster.remove(i);
i--; // you have to decrement this value to account for the missing item
studentFound = true; // student with desired ID is removed
}
if (!studentFound) System.out.println("Student with ID "+StudentID+" was not found");
}
答案 4 :(得分：0)
是的，你可以这样做，请在学生班上添加一些东西
public class Student {
private int StudentID;
private String FirstName;
private String LastName;
private String Email;
private int age;
private int[] Grades;
public Student(int S_ID ){
this.setStudentID(S_ID);
}
//Constructor
public Student(int S_ID,String fName,String lName,String email,int Age,
int[] grade){
setStudentID(S_ID);
setFirstName(fName);
setLastName(lName);
setEmail(email);
setAge(Age);
setGrade(grade);
}
//Accessor Methods (get methods)
public int getStudentID(){
return StudentID;
}
public String getFirstName(){
return FirstName;
}
public String getLastName(){
return LastName;
}
public String getEmail(){
return Email;
}
public int getAge(){
return age;
}
public int[] getGrades(){
return Grades;
}
//Mutator methods (set methods)
public void setStudentID(int StudentID){
this.StudentID=StudentID;
}
public void setFirstName(String FirstName){
this.FirstName=FirstName;
}
public void setLastName(String LastName){
this.LastName=LastName;
}
public void setEmail(String Email){
this.Email=Email;
}
public void setAge(int age){
this.age=age;
}
public void setGrade(int Grade[]){
this.Grades=Grade;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Student student = (Student) o;
return StudentID == student.StudentID;
}
@Override
public int hashCode() {
return StudentID;
}
}
在主要区域课程中你可以做到
public class Test {
public static void main(String []args){
List<Student> list = new ArrayList<>();
list.add(new Student(1,"a","a","a",1, new int[]{1}));
list.add(new Student(2,"b","b","b",2, new int[]{2}));
list.remove(new Student(1));
list.forEach(System.out::println);
}
}
<强>输出
com.traveliko.platform.web.frontend.Student@2