如何将输入字符串“ BBBB”与上述ArrayList中的学校进行比较？

Question

Let say I have an ArrayList<Student> contains 4 Students(name , city, school) . For example:

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

If user enter “BBBB” then it displays: :

 1. John    Nevada   BBBB
 2. Ty      Artes    BBBB

My question is that how do I compare a input string “BBBB” with the schools in the above ArrayList ? Thank you for any help that you guys would provide!

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

Assuming your student is modelled like this (AAAA, BBBB values are stored in blah field):

public class Student {

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

  //getters & setters..

}

The simplest (not most efficient way) is just to loop the array list and compare the query string with value of blah field

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

Answer 2

I believe Student is class and you are creating list of Student

The ArrayList uses the equals method implemented in the class (your case Student class) to do the equals comparison.

You can call contains methods of list to get matching object

Like,

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;
  }
}

Your array list would be like this

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.

Or,

You can simply iterate object in studentList and compare items

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

  }
}

Or, as you commented ,

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.
        }
    }
}

Or,

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

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

or even,

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

So now you have set of options

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

Answer 3

I would probably use Guava library from Google.
Take a look at this question: What is the best way to filter a Java Collection? It provides many excelent solutions for your problem.