Im creating a program that is supposed have the user enter a student name and see if it exist in the student array using a linear search method. The student array is in a different class and im having trouble creating a constructor i have tried many things and its not working can someone point me in the right direction.
My linear search class is
import java.util.*;
import java.util.Scanner;
public class LinearSearch {
public int find(Student [] a, String nm) {
for (int i = 0; i < a.length; i++) {
if (a[i].equals(nm)){
return i;
break;
}
else{
return -1;
}
}
}
public static void main(String[] args) {
Scanner reader = new Scanner(System.in);
LinearSearch search = new LinearSearch();
Student stu = new Student();
Student [] arr = stu.getArray();
System.out.print("Enter the name to search: ");
String name = reader.nextLine();
int n = search.find(arr, name);
if ((n >= 0) && (n < arr.length)) {
System.out.println(name + " was found at index: " + n);
} else {
System.out.println(name + " was not found");
}
}
}
My Student class is
import java.util.*;
public class Student {
public Student(){
}
public Student [] getArray(){
Student [] studentArray = new Student[3];
studentArray[0] = new Student ("Mel");
studentArray[1] = new Student ("Jared");
studentArray[2] = new Student ("Mikey");
return studentArray;
}
}
You defined a constructor with no argument:
public Student() {
}
But you're invoking a constructor which needs a String as argument:
studentArray[0] = new Student("Mel");
So, your constructor should have a String as argument:
public Student(String name)
And you should probably store this name as a field in the Student class:
private String name;
public Student(String name) {
this.name = name;
}
Note that there is no way that a Student instance could be equal to a String instance. You should provide a getter method for the name, and compare the entered String with the name of the student, instead of comparing it with the student itself.
import java.util.*;
public class Student {
private String name;
public Student(String name){
this.name = name;
}
public Student [] getArray(){
Student [] studentArray = new Student[3];
studentArray[0] = new Student ("Mel");
studentArray[1] = new Student ("Jared");
studentArray[2] = new Student ("Mikey");
return studentArray;
}
public String getName(){
return name;
}
}
and of course in the compersion you'll need to do:
f (a[i].getName().equals(nm)){
public class Student {
private String studentName;
private Student[] studentArray;
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public Student[] getStudentArray() {
return studentArray;
}
public void setStudentArray(Student[] studentArray) {
this.studentArray = studentArray;
}
public Student(){
studentArray = new Student[3];
}
public Student[] getArray() {
Student st1 = new Student();
st1.setStudentName("mel");
Student st2 = new Student();
st2.setStudentName("Jared");
Student st3 = new Student();
st3.setStudentName("Mikey");
studentArray[0]=st1;
studentArray[1]=st2;
studentArray[2]=st3;
return studentArray;
}
}
the above code is your Student class. there is no need to create a constructor though. but because you would like it i put it in the code.
the LinearSearch class is as follow:
public class LinearSearch {
private int i;
public int find(Student[] a, String nm) {
for ( i = 0; i < a.length; i++) {
if (a[i].getStudentName().equals(nm)) {
break;
} else {
i = -1;
}
}
return i;
}
public static void main(String[] args) {
Scanner reader = new Scanner(System.in);
LinearSearch search = new LinearSearch();
Student stu = new Student();
Student[] arr = stu.getArray();
System.out.print("Enter the name to search: ");
String name = reader.nextLine();
int n = search.find(arr, name);
if ((n >= 0) && (n < arr.length)) {
System.out.println(name + " was found at index: " + n);
} else {
System.out.println(name + " was not found");
}
}
}
Related
I am new in java and I trying to get information
for five students and save them into an array of classes. how can I do this?
I want to use class person for five students whit different informations
import java.io.IOException;
import java.util.*;
public class exam
{
public static void main(String[] args)
{
Scanner s = new Scanner(System.in);
// I want to get and save information in this array
person[] f = new student[5];
}
}
class person defined for get name and family name.
import java.util.*;
public abstract class person {
Scanner scr = new Scanner(System.in);
private String name , fname;
public void SetName() {
System.out.println("enter name and familyNAme :");
name = scr.next();
}
public String getname() {
return name;
}
public void setfname () {
System.out.println("enter familyname:");
fname = scr.next();
}
public String getfname() {
return fname;
}
}
class student that inherits from the class person for get studentID and student Scores .
import java.util.*;
class student extends person {
float[] p = new float[5];
int id , sum ;
float min;
public void inputs() {
System.out.println("enter the id :");
id = scr.nextInt();
}
public void sumation() {
System.out.println("enter points of student:");
sum= 0;
for(int i = 0 ; i<5 ; i++){
p[i]=scr.nextFloat();
sum+=p[i];
}
}
public void miangin() {
min = (float)sum/4;
}
}
So first things first, when creating Java objects, refrain from getting input inside the object so that if you decide to change the way you get input (e.g. transition from command line to GUI) you don't need to modify the Java object.
Second, getters and setters should only get or set. This would save some confusion when debugging since we don't have to check these methods/functions.
So here's the person object:
public abstract class Person {
protected String name, fname;
public Person (String name, String fname) {
this.name = name;
this.fname = fname;
}
public void setName (String name) {
this.name = name;
}
public String getName () {
return name;
}
public void setFname (String fname) {
this.fname = fname;
}
public String getFname () {
return fname;
}
}
And here's the student object (tip: you can make as much constructors as you want to make object creation easier for you):
public class Student extends Person {
private float[] p;
private int id;
public Student (String name, String fname) {
this (name, fname, -1, null);
}
public Student (String name, String fname, int id, float[] p) {
super (name, fname);
this.id = id;
this.p = p;
}
public void setP (float[] p) {
this.p = p;
}
public float[] getP () {
return p;
}
public void setId (int id) {
this.id = id;
}
public int getId () {
return id;
}
public float summation () {
float sum = 0;
for (int i = 0; i < p.length; i++)
sum += p[i];
return sum;
}
public float miangin () {
return summation () / 4.0f;
}
#Override
public String toString () {
return new StringBuilder ()
.append ("Name: ").append (name)
.append (" Family name: ").append (fname)
.append (" Id: ").append (id)
.append (" min: ").append (miangin ())
.toString ();
}
}
And lastly, wherever your main method is, that is where you should get input from. Take note that when you make an array, each index is initialized to null so you still need to instantiate each array index before using. I made a sample below but you can modify it depending on what you need.
import java.util.*;
public class Exam {
Scanner sc;
Person[] people;
Exam () {
sc = new Scanner (System.in);
people = new Person[5];
}
public void getInput () {
for (int i = 0; i < people.length; i++) {
System.out.print ("Enter name: ");
String name = sc.nextLine ();
System.out.print ("Enter family name: ");
String fname = sc.nextLine ();
System.out.print ("Enter id: ");
int id = sc.nextInt (); sc.nextLine ();
System.out.println ("Enter points: ");
float[] points = new float[5];
for (int j = 0; j < points.length; j++) {
System.out.printf ("[%d] ", j + 1);
points[j] = sc.nextFloat (); sc.nextLine ();
}
people[i] = new Student (name, fname, id, points);
}
}
public void printInput () {
for (Person p: people)
System.out.println (p);
}
public void run () {
getInput ();
printInput ();
}
public static void main (String[] args) {
new Exam ().run ();
}
}
Just one last tip, if you ever need dynamic arrays in Java, check out ArrayList.
You can add a class attribute, and then add class information for each student, or you can add a class class, define an array of students in the class class, and add an add student attribute, and you can add students to that class.
First of all, please write class names with capital letter (Student, Exam <...>).
Exam class:
import java.util.Scanner;
public class Exam {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
Student[] students = new Student[]{
new Student(),
new Student(),
new Student(),
new Student(),
new Student()
};
for (int i = 0; i < 5; i++) {
students[i].setFirstName();
students[i].setLastName();
students[i].setId();
}
}
}
Person class:
import java.util.Scanner;
public class Person {
String firstName, lastName;
public String getFirstName() {
return firstName;
}
public void setFirstName() {
System.out.println("Type firstName: ");
this.firstName = new Scanner(System.in).next();
}
public String getLastName() {
return lastName;
}
public void setLastName() {
System.out.println("Type lastName: ");
this.lastName = new Scanner(System.in).next();
}
}
Student class:
import java.util.Scanner;
public class Student extends Person{
int id;
public int getId() {
return id;
}
public void setId() {
//Converting String line into Integer by Integer.parseInt(String s)
System.out.println("Type id: ");
this.id = Integer.parseInt(new Scanner(System.in).next());
}
}
I'm having a number of issues with this:
1) Under which class would I want to put my Scanner, so that it assigns the proper variables? The task I am given says to "read data file into Students" in the Tester class
2) How can I make a readFile() method in the Students class?
3) How can I properly write toString() in both Student and Students classes?
import java.io.*;
import java.util.*;
public class Tester
{
public static void main(String args[]) throws IOException
{
//new Students object
Students theStudents = new Students();
//reads file from Students
theStudents.readFile();
// create new 'Output.txt' file to save program output
PrintWriter ot = new PrintWriter(new FileWriter("Output.txt"));
System.out.println(theStudents.toString());
ot.println(theStudents.toString());
ot.close();
}
}
import java.util.ArrayList;
import java.io.*;
import java.util.*;
import java.io.FileReader;
public class Students
{
// instance variables
private ArrayList<Student> students;
public Students()
{
//create arraylist for students
students = new ArrayList<>();
}
public void readFile() throws IOException
{
String name;
int age;
double gpa;
String line;
//Scanner to read file
try {
Scanner sc = new Scanner(new File("Students.txt"));
while (sc.hasNextLine()) {
name = sc.nextLine();
line = sc.nextLine();
age = Integer.parseInt(line);
line = sc.nextLine();
gpa = Double.parseDouble(line);
}
}
catch (FileNotFoundException e) {
System.out.println("Error");
}
}
public void add(Student s)
{
students.add(s);
}
public Students aboveAverage(double avgGPA)
{
Students aboveAverage = new Students();
for (int i = 0; i < students.size(); ++i) {
if (students.get(i).getGPA() > avgGPA)
aboveAverage.add(students.get(i));
}
return aboveAverage;
}
public String toString()
{
String out = "";
int count = 0;
for (Student student : students){
out += students.toString() + " ";
++count;
}
return out;
}
}
public class Student
{
private String name;
private int age;
private double gpa;
public Student(String studentName, int studentAge, double studentGPA)
{
name = studentName;
age = studentAge;
gpa = studentGPA;
}
public String getName()
{
return name;
}
public int getAge()
{
return age;
}
public double getGPA()
{
return gpa;
}
public String toString()
{
return String.format("%10s", name) +
String.format("%5d", age) + String.format("%10.2f \n", gpa);
}
}
I'm not gonna give you the complete solution but here is a way to approach this problem.
You need readLine() instead of nextLine()
Once you read the values, you need to call the add() function with the Student Object to add it to your ArrayList.
Code Snippet:
try (Scanner sc = new Scanner(new File("Students.txt"))) {
while (sc.hasNextLine()) {
String name = sc.readLine();
int age = Integer.parseInt(sc.readLine());
double gpa = Double.parseDouble(sc.readLine());
/* Create A New Student Object & Add To List */
add(new Student(name, age, gpa));
}
} catch (FileNotFoundException e) {
System.out.println("Error");
}
Also, you need to #Override the toString() function.
I have two classes; Course and Student classes. One of the fields in the Student class is a course. When i run this program, I fail to hold a course object in the declared array. The code below will give more light where things are failing:
package school;
public class Course
{
private String courseName;
private String courseGrade;
int counter;
public Course()
{
courseName="";
courseGrade="";
counter = 0;
}
public Course (String name,String grade)
{
courseName=name;
courseGrade=grade;
counter=0;
}
public String getCourseName()
{
return courseName;
}
public String getCourseGrade()
{
return courseGrade;
}
public void setCourse(String name,String grade)
{
courseName=name;
courseGrade=grade;
counter++;
}
#Override
public String toString ()
{
return String.format("%-10s %-10s", courseName,courseGrade);
}
}
package school;
public class Student
{
private String firstName;
private String lastName;
private int counter;
private Course [] myCourse;
public Student ()
{
firstName="";
lastName="";
myCourse =new Course[2];
for (int i=0;i<2;i++)
{
myCourse [i]= new Course ();
}
counter= 0;
}
public Student(String first,String last)
{
firstName=first;
lastName=last;
myCourse =new Course[2];
for (int i=0;i<2;i++)
{
myCourse [i]= new Course ();
}
counter= 0;
}
public Student(String first,String last, Course [] newCourse)
{
firstName=first;
lastName=last;
myCourse= new Course [2];
for (int i=0;i<2;i++)
{
myCourse [i]= new Course ();
}
counter++;
}
public String getFirstName()
{
return firstName;
}
public String getLastName()
{
return lastName;
}
public int getNumberOfCourses()
{
return counter;
}
public void setStudent(String first,String last, Course [] newCourse)
{
firstName=first;
lastName=last;
myCourse= new Course [2];
for (int i=0;i<2;i++)
{
myCourse [i]= newCourse[i];
}
counter++;
}
public void setStudent(String first,String last)
{
firstName=first;
lastName=last;
}
public void registerCourses(Course newCourse)
{
for (int i=0;i<2;i++)
{
myCourse[i]=newCourse;
}
counter++;
}
public String toString()
{
String getString;
getString =(firstName+" "+lastName);
for(int i=0;i<2;i++)
{
getString=getString+String.format("%n %-10s",myCourse[i]);
}
return getString;
}
}
package school;
import java.util.*;
public class Test
{
static Scanner cin= new Scanner(System.in);
public static void main(String[] args)
{
String first,last,name,grade;
Student [] myStudent= new Student [2];
Course [] myCourse= new Course [2];
for (int i=0;i<2;i++)
{
myStudent[i] = new Student();
System.out.println("enter name:");
first=cin.next();
System.out.println("Last Name:");
last=cin.next();
// For loop within a for loop
for (int j=0;j<2;j++)
{
myCourse [j]= new Course ();
System.out.println("Course Name:");
name=cin.next();
System.out.println("Course Grade:");
grade=cin.next();
myCourse [j] = new Course(name,grade);
myStudent[i].registerCourses(myCourse [j]);
}
myStudent [i]=new Student(first, last, myCourse);
}
for (int i=0;i<2;i++)
{
System.out.println(myStudent[i]);
}
}
}
the problem is in the second for loop which is unable to hold course object that i want it to.
I want the program to output something similar to the following:
Student One
MAT A
PHY B
BIO C
CHE A
LAN A+
HIS A
Student Two
COM C
Statistics A+
COM C
Mathematics D
Geography A
Biology C+
Student Three
Biology C
Mathematics D
LAN A+
COM B
Physics B
Physics B
However I am unable to obtain that output. In fact i get the following output:
enter name:
Student
Last Name:
One
Course Name:
MAT
Course Grade:
A
Course Name:
COM
Course Grade:
C
enter name:
Student
Last Name:
Two
Course Name:
STA
Course Grade:
A
Course Name:
ENG
Course Grade:
B
Student One
Student Two
you are destroying the first myStudent[i] data when performing a new on the same index at the end of your loop:
for (int i=0;i<2;i++)
{
myStudent[i] = new Student();
<some code>
myStudent [i]=new Student(first, last, myCourse);
Since you have an undefined number of courses I would suggest using ArrayList and then you do
Also, think what you are doing here.
public void registerCourses(Course newCourse)
{
for (int i=0;i<2;i++)
{
myCourse[i]=newCourse;
}
counter++;
}
You are adding one course and then saying for each position for a course in my array add the new course I was given
You should either use an index, or use an arraylist, or linkedlist etc.
E.g.
public void registerCourses(Course newCourse, int index)
{
myCourse[index]=newCourse;
}
or
public void registerCourses(Course newCourse)
{
myCourse.push(newCourse); // that is given myCourse is an ArrayList<Course>
}
Check the registerCourses method inside Student class. It seems its overriding your result on a same index.
You can do that with List and keep adding that.
Here is the one I updated Student Class.
package com.stack;
import java.util.ArrayList;
import java.util.List;
public class Student
{
private String firstName;
private String lastName;
private int counter;
private List<Course> myCourse;
public Student ()
{
firstName="";
lastName="";
myCourse =new ArrayList<Course>();
counter= 0;
}
public Student(String first,String last)
{
firstName=first;
lastName=last;
myCourse =new ArrayList<Course>();
counter= 0;
}
public Student(String first,String last, List<Course> newCourse)
{
firstName=first;
lastName=last;
myCourse= newCourse;
counter++;
}
public String getFirstName()
{
return firstName;
}
public String getLastName()
{
return lastName;
}
public int getNumberOfCourses()
{
return counter;
}
public void setStudent(String first,String last, List<Course> newCourse)
{
firstName=first;
lastName=last;
myCourse= newCourse;
counter++;
}
public void setStudent(String first,String last)
{
firstName=first;
lastName=last;
}
public void registerCourses(Course newCourse)
{
myCourse.add(newCourse);
counter++;
}
public String toString()
{
String getString;
getString =(firstName+" "+lastName);
for(int i=0;i<2;i++)
{
getString=getString+String.format("%n %-10s",myCourse.get(i));
}
return getString;
}
}
Test Class:
package com.stack;
import java.util.*;
public class Test
{
static Scanner cin= new Scanner(System.in);
public static void main(String[] args)
{
String first,last,name,grade;
Student [] myStudent= new Student [2];
List<Course> myCourse= new ArrayList<Course>();
for (int i=0;i<2;i++)
{
myStudent[i] = new Student();
System.out.println("enter name:");
first=cin.next();
System.out.println("Last Name:");
last=cin.next();
// For loop within a for loop
for (int j=0;j<2;j++)
{
System.out.println("Course Name:");
name=cin.next();
System.out.println("Course Grade:");
grade=cin.next();
Course myC = new Course(name,grade);
myCourse.add(myC);
myStudent[i].registerCourses(myC);
}
myStudent [i]=new Student(first, last, myCourse);
}
for (int i=0;i<2;i++)
{
System.out.println(myStudent[i]);
}
}
}
Note: For 3 Students, you need to iterate loop until i<3 (not 2).
I have two different class, Student and StudentTest - the Student class has;
public class Student {
// Data Members
private String name; // The name of this student
private long idNumber; // The ID number of this student
// Constructs a new Student with passed name and ID number parameters.
public Student(String studentName, long studentIDNumber) {
name = studentName;
idNumber = studentIDNumber;
}
// Returns the name of this student.
public String getName() {
return name;
}
// Returns the ID number of this student.
public long getIDNumber() {
return idNumber;
}
// Sets the name of this student.
public void setName(String studentName) {
name = studentName;
}
// Sets the ID number of this student.
public void setIDNumber(long studentIDNumber) {
idNumber = studentIDNumber;
}
#Override
public String toString(){
return "Name: " + this.name;
}
} // end class
And the StudentTest class has 3 different methods, 1. to ask the user to enter the size of an array and then create an array of type Student, 2. to ask the user to populate the array with names and ID numbers, 3. to display the contents of the array.
import java.util.Scanner;
public class StudentTest {
// Main method.
public static void main(String [] args) {
Student[] students = createArray();
populateArray(students);
displayArray(students);
}
// Method that asks user for size of array.
public static Student[] createArray() {
System.out.println("Enter size of array: ");
Scanner userInputEntry = new Scanner(System.in);
int inputLength = userInputEntry.nextInt();
Student students[] = new Student[inputLength];
return students;
}
// Method that asks user to populate array.
public static void populateArray(Student [] array) {
for(int i = 0; i < array.length; i++) {
array[i] = new Student();
System.out.println("Enter student name: ");
Scanner userInputEntry = new Scanner(System.in);
array[i].setName(userInputEntry.next());
System.out.println("Enter student ID number: ");
array[i].setIDNumber(userInputEntry.nextLong());
}
}
// Method that displays contents of array.
public static void displayArray(Student[] array) {
for(int i = 0; i < array.length; i++){
System.out.println(array[i].toString());
}
}
}
When I try to run it, I get an error about the
array[i] = new Student();
in the for loop in the second method.
How would you expect this to work ?
#Override
public void toString(){
return "Name: " + this.name;
}
It should give you an compile error. You are trying to send a string back and the return type is void.
Change it to
#Override
public String toString(){
return "Name: " + this.name;
}
Change you main method to
// Main method.
public static void main(String [] args) {
Student[] students = createArray();
populateArray(students);
displayArray(students)
}
I am new to java and doing some arraylist work, and when compiling my lists just return null values instead of names I have typed in.
I don't understand why this is so, so if anyone could advise/help me that would be great.
Here is my main code
import java.util.*;
public class StudentData
{
public static void main(String[] args)
{
Scanner in = new Scanner(System.in);
ArrayList<Student> studentList = new ArrayList<Student>();
String yesNo = "true";
do
{
System.out.println("Enter student's name: ");
String name = in.next();
Student s = new Student();
studentList.add(s);
String input;
do
{
System.out.println("Would you like to enter data for another student? Yes/No ");
yesNo = in.next();
}
while (!yesNo.equalsIgnoreCase("YES") && !yesNo.equalsIgnoreCase("NO"));
}
while (yesNo.equalsIgnoreCase("YES"));
for(int i = 0; i < studentList.size(); i++)
{
System.out.println(studentList.get(i).getName());
}
}
}
And
class Student
{
private String studentName;
public StudentData(String name)
{
setName(name);
}
public String getName()
{
return studentName;
}
public void setName(String name)
{
studentName = name;
}
}
You're creating a student but didn't set the name :
String name = in.next();
Student s = new Student();
studentList.add(s);
Try with :
String name = in.next();
Student s = new Student();
s.setName(name);
studentList.add(s);
Also replace your constructor. I.e :
public StudentData(String name){
setName(name);
}
should be
public Student(String name) {
setName(name);
}
Then you will be able to do Student s = new Student(name);