如何將輸入字符串“ BBBB”與上述ArrayList中的學校進行比較？

Question

假設我有一個ArrayList<Student>包含4個Students(name , city, school) 。 例如：

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

如果用戶輸入“ BBBB”，則顯示：：

 1. John    Nevada   BBBB
 2. Ty      Artes    BBBB

我的問題是如何將輸入字符串“ BBBB”與上面的ArrayList的學校進行比較？ 感謝您提供的任何幫助！

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

假設您的學生是這樣建模的（AAAA，BBBB值存儲在blah字段中）：

public class Student {

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

  //getters & setters..

}

最簡單（不是最有效的方法）只是循環數組列表，並將查詢字符串與blah字段的值進行比較

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

Answer 2

我相信Student is class ，您正在創建Student列表

該ArrayList使用equals的類（你的情況下，學生類）實現的方法做等於比較。

您可以調用包含列表的方法來獲取匹配的對象

喜歡，

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;
  }
}

您的數組列表將如下所示

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，

您可以簡單地迭代studentList對象並比較項目

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

  }
}

或者，正如您評論的那樣，

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++;
}

所以現在您有了一些選擇

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

Answer 3

我可能會使用Google的Guava庫。
看一下這個問題： 過濾Java集合的最佳方法是什么？ 它為您的問題提供了許多出色的解決方案。