如何将输入字符串“ BBBB”与上述ArrayList中的学校进行比较？

Question

假设我有一个ArrayList<Student>包含4个Students(name , city, school) 。 例如：

 1. John   Nevada   BBBB
 2. Mary   Ander    AAAA
 3. Winn   Arcata   CCCC
 4. Ty     Artes    BBBB

如果用户输入“ BBBB”，则显示：：

 1. John    Nevada   BBBB
 2. Ty      Artes    BBBB

我的问题是如何将输入字符串“ BBBB”与上面的ArrayList的学校进行比较？ 感谢您提供的任何帮助！

public class Student
{
    private String name;
    private String city;
    private String school;

    /**
     * Constructor for objects of class Student
     */
    public Student(String name, String city, String school)
    {
       this.name = name;
       this.city = city;
       this.school = school;
    }

    public String getSchool(String school)
    {
        return this.school = school;
    }

     public String toString()
    {
        return  "Name: " + name + "\tCity: " +city+ "\tSchool: "+school;
    }


}


public class AllStudent
{
    // instance variables - replace the example below with your own
    private ArrayList<Student> listStudent = new ArrayList<Student>();

    /**
     * Constructor for objects of class AllStudent
     */
    public AllStudent() throws IOException
    {

        //variables
        // read an input file and save it as an Arraylist
        fileScan = new Scanner (new File("students.txt");
        while(fileScan.hasNext())
        {
            //.......
            listStudent.add(new Student(name,city,school);
     }
     //now let user enter a school, the display name, city, school of that student.
     //i am expecting something like below...
     public void displayStudentBasedOnSchool(String school)
     {
       for (i = 0; i < listStudent.size(); i++)
       {
        //what should i put i here to comapre in input School with school in the listStudent>
        }
     }
}

Answer 1

假设您的学生是这样建模的（AAAA，BBBB值存储在blah字段中）：

public class Student {

  private String name;
  private String state;
  private String blah;

  //getters & setters..

}

最简单（不是最有效的方法）只是循环数组列表，并将查询字符串与blah字段的值进行比较

for(Student s : studentList) {
  if(s.getBlah().equals(queryString)) {
    // match!..
  }
}

Answer 2

我相信Student is class ，您正在创建Student列表

该ArrayList使用equals的类（你的情况下，学生类）实现的方法做等于比较。

您可以调用包含列表的方法来获取匹配的对象

喜欢，

public class Student {
  private String name;
  private String city;
  private String school;
  ....   

  public Student(String name, String city, String school) {
      this.name = name;
      this.city = city;
      this.school = school;
  }

   //getters & setters..
  public String setSchool(String school) {
      this.school = school;
  }

  public String getSchool() {
      return this.school;
  }

  public boolean equals(Object other) {
      if (other == null) return false;
      if (other == this) return true;

      if (!(other instanceof Student)) return false;
      Student s = (Student)other;

      if (s.getSchool().equals(this.getSchool())) {
          return true; // here you compare school name
      } 
      return false;
  }

  public String toString() {
      return  "Name: " + this.name + "\tCity: " + this.city + "\tSchool: "+ this.school;
  }
}

您的数组列表将如下所示

ArrayList<Student> studentList = new ArrayList<Student>();  

Student s1 = new Student(x, y, z);
Student s2 = new Student(a, b, c);  

studentList.add(s1);
studentList.add(s2);

Student s3 = new Student(x, y, z); //object to search

if(studentList.contains(s3)) {
    System.out.println(s3.toString()); //print object if object exists;
} // check if `studentList` contains `student3` with city `y`.It will internally call your equals method to compare items in list.

要么，

您可以简单地迭代studentList对象并比较项目

for(Student s : studentList) {
  if(s.getSchool().equals(schoolToSearch)) {
    // print object here!..

  }
}

或者，正如您评论的那样，

public void displayStudentBasedOnSchool(String school){
    for(int i = 0; i < studentList.size(); ++i) {
        if(studentList.get(i).getSchool().equals(school)) {
            System.out.println(studentList.get(i).toString()); // here studentList.get(i) returns Student Object.
        }
    }
}

要么，

ListIterator<Student> listIterator = studentList.listIterator(); //use list Iterator

while(listIterator.hasNext()) {
    if(iterator.next().getSchool().equals(school)) {
        System.out.println(listIterator.next());
        break;
    }
}

甚至，

int j = 0;
while (studentList.size() > j) {
    if(studentList.get(j).getSchool().equals(school)){
        System.out.println(studentList.get(j));
        break;
    }
    j++;
}

所以现在您有了一些选择

1. for-loop
2. for-each循环
3. while循环
4. iterator

Answer 3

我可能会使用Google的Guava库。
看一下这个问题： 过滤Java集合的最佳方法是什么？ 它为您的问题提供了许多出色的解决方案。