Question

Binary files are convenient to computers because they’re easily machine readable. Text files are human readable, but require parsing and conversion to process in the computer. Consider a class Person that has the following structure:

public class Student {
    private String name;
    private int age;
    private double gpa;

    public Student() {
    }

    public Student(String name, int age, double gpa) {
        this.name = name;
        this.age = age;
        this.gpa = gpa;
    }

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return this.age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public double getGpa() {
        return this.gpa;
    }

    public void setGpa(double gpa) {
        this.gpa = gpa;
    }

    public String toString() {
        StringBuilder builder = new StringBuilder();
        builder.append("Student{");
        builder.append(String.format("%s=%s", "name", name));
        builder.append(String.format(",%s=%d", "age", age));
        builder.append(String.format(",%s=%.2f", "gpa", gpa));
        builder.append("}");
        return builder.toString();
    }
    
    @Override
    public boolean equals(Object obj) {
        if (obj != null && obj instanceof Student) {
            return equals((Student)obj);
        }
        return false;
    }
    
    public boolean equals(Student other) {
        if (other == null) {
            return false;
        }
        return name.equals(other.name) &&
            age == other.age &&
            Math.abs(gpa - other.gpa) < 0.0001;
    }
}

A number of student records were written out to a file using the toString() method given above. Roughly, they look like the following:

Student{name=Joe O'Sullivan,age=22,gpa=3.14}
Student(name=Jane Robinson,age=19,gpa=3.81}
....
Student{name=Jill Gall,age=21,gpa=2.98}

Your task is to implement a method that will return an array of Students based on a parameter file name that is passed into the method. You will open the text file, read lines, split lines into fields, and then call the setters based on the key/value pairs in the string. Fields will always be in the same order: name, age, gpa. The array should be exactly the same size as the number of lines in the file you are reading. At most, there will be 20 lines in the file. You should not throw any exceptions from the function. if the file doesn't exist, return a zero-length array.

Some hints:

• You can use the File class to connect the name to the file on disk.
• You can create a Scanner object by passing in the File to read lines.
• You can use the split() method of String to take a line from the file and break it up based on delimiters You may need to do this multiple times (e.g. once on a comma, and then on an equals sign).
• To convert from string data to integer data, use Integer.parseInt(). You can do the same with doubles and Double.parseDouble()

Answer 1

/////////////////////////////////////////////////

public class Student {
private String name;
private int age;
private double gpa;

public Student() {
}

public Student(String name, int age, double gpa) {
this.name = name;
this.age = age;
this.gpa = gpa;
}

public String getName() {
return this.name;
}

public void setName(String name) {
this.name = name;
}

public int getAge() {
return this.age;
}

public void setAge(int age) {
this.age = age;
}

public double getGpa() {
return this.gpa;
}

public void setGpa(double gpa) {
this.gpa = gpa;
}

public String toString() {
StringBuilder builder = new StringBuilder();
builder.append("Student{");
builder.append(String.format("%s=%s", "name", name));
builder.append(String.format(",%s=%d", "age", age));
builder.append(String.format(",%s=%.2f", "gpa", gpa));
builder.append("}");
return builder.toString();
}
  
@Override
public boolean equals(Object obj) {
if (obj != null && obj instanceof Student) {
return equals((Student)obj);
}
return false;
}
  
public boolean equals(Student other) {
if (other == null) {
return false;
}
return name.equals(other.name) &&
age == other.age &&
Math.abs(gpa - other.gpa) < 0.0001;
}
}

/////////////////////////////////////////

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.Scanner;

public class StudentTest {
  
   public static Student [] studentList(String filename){

       // first get the number of valid lines in this file
       int index=0;// to store number of lines
       BufferedReader br1=null;         
       String line="";
      
       try {
           // read file
           br1=new BufferedReader(new FileReader(filename));
             
           // read each file
           while((line=br1.readLine())!=null){
               String [] spltreslt=line.split(",");
               // if line is valid , then increase index
               if(spltreslt.length==3){
                   index++;
               }
           }
           br1.close();
       } catch (IOException e) {}
      
      
       // if valid line exist
       // the create array and load data in array
       if(index>0){
           Student [] students=new Student[index];
           index=0;
           BufferedReader br=null;             
          
           try {
               br=new BufferedReader(new FileReader(filename));
               // read line by line from file
               while((line=br.readLine())!=null){
                   // split line
                   String [] spltreslt=line.split(",");
                   // if line is valid
                   if(spltreslt.length==3){
                       // create new student object
                       Student stdnt=new Student();
                       // split each and set data to student object
                       stdnt.setName(spltreslt[0].split("=")[1]);
                       stdnt.setAge(Integer.parseInt(spltreslt[1].split("=")[1]));
                         
                       // gpa=2.98}
                       // split by "=" [ after spiting 2nd string hold 2.98} ]
                       // represented by split("=")[1]
                       // 2.98} , this string split again by "}"
                       // [ after spiting 1st string hold 2.98 ]
                       // represented by split("}")[0]
                         
                       stdnt.setGpa(Double.parseDouble(spltreslt[2].split("=")[1].split("}")[0]));
                       // add in student array
                       students[index++]=stdnt;                         
                   }
               }
               br.close();
           } catch (IOException e) {}
           // return array
           return students;
       }
       else{
           // return array of length 0
           return null;
       }      
   }
  
  
   public static void main(String [] args){
       Scanner sc=new Scanner(System.in);
       // take file name from user
       System.out.print("Enter the file name : ");
       String filename=sc.next();
       sc.close();
      
       // load data from file and save in array
       Student [] students=studentList(filename);
         
       // display each student data
       for(int i=0;i<students.length;i++){
           System.out.println(students[i]);
       }
   }
}