Question

用户输入课程编号，我需要知道如何搜索列表中的对象，看看该输入是否与列表中任何对象的课程编号匹配。

这是控制器代码

import java.util.*;
import java.lang.*;
import java.math.*;
import java.io.*;

public class CourseApp 
{
public static void main(String[] args) 
{
    List<Course> courses = new ArrayList<Course>();

    IO IO = new IO();

    String number = "";
    String name = "";

    String FName = "";
    String LName = "";
    String UName = "";

    String title = "";
    String author = "";
    double price = 0.0;

    String reply = "";

    String delete = "";

    //add objects to list
    do {
        IO.newLine();

        number = IO.courseNumber();

        name = IO.courseName();

        FName = IO.instrFName();
        LName = IO.instrLName();
        UName = IO.instrUName();

        Instructor tempInstr = new Instructor(LName, FName, UName);

        title = IO.bookTitle();
        author = IO.bookAuthor();
        price = IO.bookPrice();

        TextBook tempBook = new TextBook(title, author, price);

        Course course = new Course(number, name, tempInstr, tempBook);

        courses.add(course);

        reply = IO.addAnother();

    } while (reply.equalsIgnoreCase ("Y"));

    IO.newLine();

    //display course
    System.out.print(courses.get(0) + "\n\n");

    for (int i = 1; i < courses.size(); i++)
    {
        System.out.println("Press enter to continue...");
        Scanner scanner = new Scanner(System.in);
        scanner.nextLine();

        System.out.print(courses.get(i) + "\n\n");
    }

    //delete course
    delete = IO.courseDelete();
    int x = 0;

    while (x < courses.size())
    {   

        Course course = new Course(courses.get(x));

        if (course.getNumber() == delete)
        {
            courses.remove(x);
            System.out.print("Course deleted.");
        }
        else
        {
            x++;
        }
    }

}
}

课程班的代码

 public class Course
 {
 private String courseNumber;    // e.g. CIS 200
 private String courseName;      // e.g. Programming Fundamentals
 private Instructor instructor;  // Course instructor (object)
 private TextBook textBook;      // Required Course textbook (object)

 /**
  This constructor initializes the courseName,
  instructor, and text fields.
  @param name The name of the course.
  @param instructor An Instructor object.
  @param text A TextBook object.
 */

 public Course(String number, String name, Instructor instr,
             TextBook text)
 {
  // Assign the courseNumber.
  courseNumber = number;

  // Assign the courseName.
  courseName = name;

  // Create a new Instructor object, passing
  // instr as an argument to the copy constructor.
  instructor = new Instructor(instr);

  // Create a new TextBook object, passing
  // text as an argument to the copy constructor.
  textBook = new TextBook(text);
 }

 public Course(Course x)
 {
   courseNumber = x.courseNumber;
   courseName = x.courseName;
   instructor = x.instructor;
   textBook = x.textBook;
 }

 /**
  getName method
  @return The name of the course.
 */

 public String getName()
 {
    return courseName;
 }

 /**
    getNumber method
    @return The number of the course.
 */

 public String getNumber()
 {
    return courseNumber;
 }
 /**
  getInstructor method
  @return A reference to a copy of this course's
          Instructor object.
*/

public Instructor getInstructor()
{
  // Return a copy of the instructor object.
  return new Instructor(instructor);
 }

/**
  getTextBook method
  @return A reference to a copy of this course's
          TextBook object.
*/

public TextBook getTextBook()
{
  // Return a copy of the textBook object.
  return new TextBook(textBook);
}

/**
  toString method
  @return A string containing the course information.
*/

public String toString()
{
   // Create a string representing the object.
  String str = "Course: " + courseNumber + ", " + courseName + "\n" + 
 "Instructor: " + instructor + "\n" + "Textbook: " + textBook;

  // Return the string.
  return str;
}
}

和IO类

/**
* IO handles all input and output for the
* four-square encryption algorithm
*
* <Add remaining required documentation here>
*/

import java.util.*;
import java.lang.*;
import java.math.*;
import java.io.*;

public class IO {
private Scanner s;

/**
 * IO sets up a new Scanner to System.in
 */
public IO() {
    s = new Scanner(System.in);
}

public String tryCatch(String message)
{
    boolean loop = false;
    String x = "";

    do
    {   
        try 
        {
            System.out.print(message);
            x = s.nextLine();

            loop = false;

            if (x.length() == 0)
            {
                loop = true;
                throw new Exception();
            }
        }
        catch (Exception e)
        {
            System.out.print("Input cannot be blank! ");
        }
    } while(loop == true);

    return x;
}

/**
 * firstKey returns the first key from the user
 *
 * @return The first key from the user
 */

public String courseNumber() {
    return tryCatch("What is the course number? ");
} 


/**
 * secondKey returns the second key from the user
 *
 * @return The second key from the user
 */
public String courseName() {
    return tryCatch("What is the course name? ");
} 

public String instrFName() {
    return tryCatch("What is the instructors first name? ");
} 

public String instrLName() {
    return tryCatch("What is the instructors last name? ");
} 

public String instrUName() {
    return tryCatch("What is the instructors user name? ");
} 

public String bookTitle() {
    return tryCatch("What is the title of the book? ");
} 

public String bookAuthor() {
    return tryCatch("Who is the author of the book? ");
} 

public String courseDelete() {
    return tryCatch("What is the course number of the course you want to delete? ");
}

public double bookPrice() {

    double x = 0.0;
    boolean loop = false;

    do{
        try 
        {
            System.out.print("What is the price of the book? ");

            x = Double.parseDouble(s.nextLine());

            loop = false;

            if (x <= 0.0)
            {
                throw new Exception();
            }
        } 
        catch (NumberFormatException ex) 
        {
            loop = true;
            System.out.print("Please enter only numbers! ");
        }
        catch (Exception e)
        {
            loop = true;
            System.out.print("Please enter only numbers greater than 0! ");
        }
    } while(loop == true);

    return x;
} 

public String addAnother() {
    return tryCatch("Add another student? ('Y' or 'N'): ");
} 

public void newLine()
{
    System.out.print("\n");
}

} // end class

以下是我试图编码我所询问的内容的部分

  //delete course
    delete = IO.courseDelete();
    int x = 0;

    while (x < courses.size())
    {   

        Course course = new Course(courses.get(x));

        if (course.getNumber() == delete)
        {
            courses.remove(x);
            System.out.print("Course deleted.");
        }
        else
        {
            x++;
        }
    }

Answer 1

在对象中实施等于：

    @Override
    public boolean equals(Object obj) {...}

使用用户的输入创建新对象
循环抛出您的对象列表，并检查您是否as.data.table(mydata)[, flag := any( stringr::str_detect( Acct_Name, keywords.list[[Segment]])), by = Acct_Name][] # Acct_Name Segment flag # 1: joes ski shop All_Other FALSE # 2: joes alarm shop All_Other TRUE # 3: joes alarm spot All_Other TRUE # 4: joes bakery All_Other FALSE # 5: joes albergue shop Apartments TRUE # 6: jims Brewery Apartments FALSE # 7: jims albergue place Apartments TRUE

您删除对象的方法并不安全，相反，您可以将List转换为Iterable，并使用最后一个删除对象，例如：

Object.equals(NewObject)

如果用户输入等于其中一个属性，则从列表中删除对象

1 个答案: