Doubly linked list for entering name and marks and print in the form of switch case

Question

Doubly linked list A runtime error is occuring it skips entering name and ask to enter marks of student It does not let me to enter student name whenever tried to show error/ output like

1. Insert at beginning
   2. Insert at end
   3. Insert at any
   4. printlist 1 Enter Student Name : Enter marks : Suraj

Exception in thread "main" java.lang.NumberFormatException: For input string: "Suraj" at java.base/jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2054)

at java.base/jdk.internal.math.FloatingDecimal.parseFloat(FloatingDecimal.java:122) at java.base/java.lang.Float.parseFloat(Float.java:455) at student_1.main(student_1.java:32)

Process finished with exit code 1

Program

 import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
class node
{
    String name;
    float marks;
    node prev;
    node next;

    public node(String name, float marks) {
        this.name = name;
        this.marks = marks;
    }
}

    public class student_1
    {
        node head;
        node last;
        public static void main(String[]args) throws IOException {
            student_1 s=new student_1();
            System.out.print("1. Insert at beginning\r\n 2. Insert at end\r\n 3. Insert at any\r\n 4. printlist\r\n");
         String name;float marks;
             BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

            char ch=(char)br.read();
            switch(ch) {
                case '1':
                    System.out.print("Enter Student Name : ");
                     name=br.readLine();
                    System.out.print("Enter marks : ");
                     marks=Float.parseFloat(br.readLine());
                s.InsBeg(name,marks);
                break;
                case '2':
                    System.out.print("Enter Student name: ");
                    name=br.readLine();br.readLine();
                    System.out.print("Enter marks : ");
                    marks=Float.parseFloat(br.readLine());
                    s.InsEnd(name,marks);
                case '3':
                    System.out.print("Enter Student name: ");
                    name=br.readLine();
                    System.out.print("Enter marks : ");
                    marks=Float.parseFloat(br.readLine());
                    s.InsEnd(name,marks);
                case '4':
                s.printlist(s.head);
            }

        }

        void InsBeg(String name, float marks)throws IOException {
            node n = new node(name, marks);
                if (head == null) {
                    head = n;
                    return;
                }

                n.prev = null;
                n.next = head;
                if (head != null) {
                    head.prev = n;

                }

                head = n;

            }


        void InsEnd(String name, float marks)throws IOException
        {
            node n=new node(name,marks);
            if(head==null)
            {head=n;
                return;
            }
           node last1=head;
            n.next=null;
            while(last1.next!=null) {
                last1 = last1.next;
            }
            last1.next=n;
            n.prev=last1;
            last=n;


        }
        public void InsAny(String name, float marks)throws IOException
        { BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
            node n=null;
            System.out.println("Position: ");
            int pos=Integer.parseInt(br.readLine());
            node prev_Node=head.prev;
            if (prev_Node == null) {
                System.out.println("The given previous node cannot be NULL ");
                return;
            }

             if(pos==1){
                 InsBeg(name, marks);return;}

                for (int i = 1; prev_Node.next!=null; ++i) {
                    if(i==pos) {
                        break;
                    }
                    prev_Node = prev_Node.next;
                }
            n.name=name;
            n.marks=marks;
            n.next = prev_Node.next;
            prev_Node.next = n;


            n.prev = prev_Node;
            if (n.next != null)
                n.next.prev = n;

        }
        public void printlist(node node)
        {
            node last = null;
            System.out.println("Traversal in forward Direction");
            System.out.print("Name "+ "\t\t\t\t\t\t"+"Marks"+"\n");
            while (node != null) {
                System.out.print(node.name + "\t\t\t\t"+node.marks+"\n");
                last = node;
                node = node.next;
            }
            System.out.println();
            System.out.println("Traversal in reverse direction");
            System.out.print("Name "+ "\t\t\t\t\t\t"+"Marks"+"\n");
            while (last != null) {
                System.out.print(last.name + "\t\t\t\t"+last.marks+"\n");
                last = last.prev;
            }
        }


    }

Answer 1

So you are facing the problem of scanner reading \n, when you press enter after choosing the option from menu. This post will give you a in-depth understanding of the problem

Add this line:

br.readLine();

after char ch=(char)br.read(); this one.

Explanation: You are using br.read() and casting it into a char. When you enter "1", what your program gets is a 1\n. Note the trailing newline character, 1 is got consumed by the read() but \n is still "hanging there". When you want to read the name like this name=br.readLine(); program reads the \n and move on.

This is the reason it is not letting you enter anything, because it read \n.

Just a side note, you may want to add a while-loop so that your program just not simply ends after first try. It should prompt user again and again until user decides to end(you can add an option to quit)