How do I know if an array list of objects contain a certain string?

user_18890007 0
Viewed 74

I made a method that search through an array list of objects. Then if the searchKey is found in the array list it will print this certain item.

Here is how I iterate through the array list if it contains the searchKey, but I just realized that it is impossible to compare a string and an object.

for(int x = 0; x < Student.students.size(); x ++){
    if(Student.students.contains(searchKey))
        System.out.print(Student.students.get(x));
}

Here's how I create the constructor and array list.

String firstName, lastName, course, yearLevel, gender;
    
    Student(String firstName, String lastName, String course, String yearLevel, String gender)
    {
        this.firstName = firstName;
        this.lastName = lastName;
        this.course = course;
        this.yearLevel = yearLevel;
        this.gender = gender;
    }

    static ArrayList<Student> students = new ArrayList<Student>();
java
3 Answers

You need to compare the one property; also you can use a for-each loop to simplify the code

for(Student s : Student.students){
    if(s.getName().equals(searchKey))
        System.out.print(s);
}

Note :

When you use a condition Student.students.contains(searchKey) in a loop, and it doesn't use the iteration variable that means there is a problem

user_72126860

You haven't defined what 'contains' means here but I'm going to assume that it means a Student contains the key if it appears as a substring in any of its String members. So let's start with a method that does that. We can define this as part of the Student class itself.

public class Student {
  .... other stuff ....
  /**
   * Return true if any of the properties of this Student
   * contain the given substring, false otherwise
   */
  public boolean contains(String s) {
    // consider addressing null cases - omitting for simplicity
    return firstName.contains(s) ||
      lastName.contains(s) ||
      course.contains(s) ||
      yearLevel.contains(s) ||
      gender.contains(s);
  }
}

Now you can iterate over your List and invoke this method to find the matches. Note that you need to handle the case that multiple Students may match a given search key (or none may match). So I would suggest collecting the results in a separate List. One does not generally iterate over Lists via the index. This example uses an enhanced for-loop (aka for-each).

public List<Student> findMatches(List<Student> students, String key) {
  List<Student> found = new ArrayList<>();
  for (Student s : students) {
    if (s.contains(key)) {
      found.add(s);
    }
  }
  return found;
}

This is a good case for using the Stream API.

public List<Student> findMatches(List<Student> students, String key) {
  return students.stream()
      .filter(s -> s.contains(key))
      .collect(Collectors.toList());
}
user_72750560

You already know comparing Object to String makes no sense. So, most probably what you are trying to do is check if any of the attributes of your Student object(name/course/year etc) has a value that matches your search key. To do that you need to convert your object into a String.

Add a toString method to your Student class which will look something like this:

public String toString() {
    return "Student [firstName=" + firstName + ", lastName=" + lastName + ", course=" + course + ", yearLevel="
            + yearLevel + ", gender=" + gender + "]";
}

Then, look for your searchKey in the string representation of your objects while iterating.

for(int x = 0; x < students.size(); x ++){
        if(students.get(x).toString().contains(searchKey))
            System.out.print(students.get(x).toString());
    }

Edit: As rightly pointed out by Jon Skeet in the comments, the default toString method will generate incorrect results, a custom implementation should be used to convert the object to String.

user_89479000
Related