从键盘（1 个值参数）或从文件（0 个值参数）读取的方法在 0 参数下无法正常工作

Question

I want my method to read triangles from keyboard or from file and then be added to ArrayList .. I have 2 classes: Point defined by 2 coordinates: int c1,int c2 , and Triangle class defined by a color string and 3 points. I have 2 methods, one in Triangle class and one in Point class:

Triangle class method:

public Triangle readingTriangle(int value) throws Exception {
        if(value == 1) {
        Scanner sc = new Scanner(System.in);
        Triangle reserve =new Triangle();
        reserve.color = sc.next();
        reserve.setA(reserve.A.readingPoint(1));
        reserve.setB(reserve.B.readingPoint(1));
        reserve.setC(reserve.C.readingPoint(1));
        return reserve;
        }
        if(value == 0) {
            Scanner input = new Scanner(new File("File"));
            Triangle reserve1 =new Triangle();

            reserve1.color=input.next();
            reserve1.setA(reserve1.A.readingPoint(0));
            reserve1.setB(reserve1.B.readingPoint(0));
            reserve1.setC(reserve1.C.readingPoint(0));
            return reserve1;
        }
        return new Triangle();


    }

Point class method:

public Point readingPoint(int value) throws Exception {
        if(value==1) {
        Scanner sc = new Scanner(System.in);
        Point reserve=new Point();
        reserve.c1 = sc.nextInt();
        reserve.c2 = sc.nextInt();
        return reserve;
        }
        if(value==0) {
            Point reserve1=new Point();
            Scanner input1 = new Scanner(new File("File"));

            input1.next();
            reserve1.c1=input1.nextInt();
            reserve1.c2=input1.nextInt();


            return reserve1;

        }
        return new Point();

    }

In test class:

    Scanner sc = new Scanner(System.in);
    int triangleNumber = sc.nextInt();
    List<Triangle> triangleList = new ArrayList<Triangle>();

    for (int i = 0; i < triangleNumber; i++) {
        Triangle t = new Triangle();
        Triangle t1 = t.readingTriangle(0);
        triangleList.add(t1);

    }
    System.out.println(triangleList);

My output:

[Triangle [color=green, A=Point [c1=20, c2=20], B=Point [c1=20, c2=20], C=Point [c1=20, c2=20]]]

My File:

green
20 20
40 40
60 60

First, I want to mention that first piece of method is working (1 value parameter is working), I have problems with reading from file. You can see the problem from output:"20 20" is given for B and C points.

I have some things that I try to respect:

• I want my structures of methods to be, if possible, respected;

• Using Scanner is mandatory(I know it's old technique);

• I don't want to change my file, because if it was a real notepad, I don't think I will stay to change things in notepad.

Other observations:

I think the problem is at scanner methods, I tried with while( input1.hasNext() ).

Answer 1

you have to use the same instance of Scanner . here you are creating a new instance in each iteration in the loop, so each time it will start from the beginning of the file. So I suggest to create a single instance in main class and pass it as parameter in your methods.

Triangle class method:

public Triangle readingTriangle(int value, Scanner sc,Scanner input) throws Exception {
    if(value == 1) {
    Triangle reserve =new Triangle();
    reserve.color = sc.next();
    reserve.setA(reserve.A.readingPoint(1,sc,input));
    reserve.setB(reserve.B.readingPoint(1,sc,input));
    reserve.setC(reserve.C.readingPoint(1,sc,input));
    return reserve;
    }
    if(value == 0) {
        Triangle reserve1 =new Triangle();

        reserve1.color=input.next();
        reserve1.setA(reserve1.A.readingPoint(0,sc,input));
        reserve1.setB(reserve1.B.readingPoint(0,sc,input));
        reserve1.setC(reserve1.C.readingPoint(0,sc,input));
        return reserve1;
    }
    return new Triangle();


}

Point class method:

public Point readingPoint(int value, Scanner sc,Scanner input) throws Exception {
    if(value==1) {
    Point reserve=new Point();
    reserve.c1 = sc.nextInt();
    reserve.c2 = sc.nextInt();
    return reserve;
    }
    if(value==0) {
        Point reserve1=new Point();
        reserve1.c1=input.nextInt();
        reserve1.c2=input.nextInt();


        return reserve1;

    }
    return new Point();

}

In test class:

Scanner sc = new Scanner(System.in); //the only time you create new instance of Scanner(System.in) -> for keybord input
Scanner input = new Scanner(new File("File"));//the only time you create new instance of Scanner(new File("File")) -> for file input

int triangleNumber = sc.nextInt();
List<Triangle> triangleList = new ArrayList<Triangle>();
for (int i = 0; i < triangleNumber; i++) {
    Triangle t = new Triangle();
    Triangle t1 = t.readingTriangle(0,sc,input);
    triangleList.add(t1);

}
System.out.println(triangleList);

Answer 2

But, if you insist to not change your parameters and keep the same structure of your actual code, you can use the method of singleton, which I do not recommend especially if you work with threads. It works fine if you're not using threads.

So to use a single instance of Scanner (or any other datatype or class), you can use the design pattern "Singleton" which consist to instantiate a single instance of your Object for the whole project.

The Singleton definition for input from keyboard (a new class) :

import java.util.Scanner;

public class ScannerSingletonKeyboard {
      private static Scanner sc = null;

    private ScannerSingletonKeyboard(){
        sc = new Scanner(System.in); 

    }

    public static Scanner getInstance(){
        if(sc==null)
             new ScannerSingletonKeyboard();
        return sc;

    }
}

The Singleton definition for input from the file (a new class) :

import java.util.Scanner;
import java.io.File;
import java.io.FileNotFoundException;

public class ScannerSingletonFile {
      private static Scanner sc = null;

    private ScannerSingletonFile(){
        try {
            Scanner sc = new Scanner(new File("File"));
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }

    }

    public static Scanner getInstance(){
        if(sc==null)
             new ScannerSingletonFile();
        return sc;

    }
}

Triangle class method:

public Triangle readingTriangle(int value) throws Exception {
    if(value == 1) {
        Scanner sc = ScannerSingletonKeyboard.getInstance();
        Triangle reserve =new Triangle();
        reserve.color = sc.next();
        reserve.setA(reserve.A.readingPoint(1));
        reserve.setB(reserve.B.readingPoint(1));
        reserve.setC(reserve.C.readingPoint(1));
        return reserve;
    }
    if(value == 0) {
        Triangle reserve1 =new Triangle();
        Scanner input = ScannerSingletonFile.getInstance();
        reserve1.color=input.next();
        reserve1.setA(reserve1.A.readingPoint(0));
        reserve1.setB(reserve1.B.readingPoint(0));
        reserve1.setC(reserve1.C.readingPoint(0));
        return reserve1;
    }
    return new Triangle();


}

Point class method:

public Point readingPoint(int value) throws Exception {
    if(value==1) {
        Scanner sc = ScannerSingletonKeyboard.getInstance();
        Point reserve=new Point();
        reserve.c1 = sc.nextInt();
        reserve.c2 = sc.nextInt();
        return reserve;
    }
    if(value==0) {
        Scanner input = ScannerSingletonFile.getInstance();
        Point reserve1=new Point();
        input.next();
        reserve1.c1=input.nextInt();
        reserve1.c2=input.nextInt();


        return reserve1;

    }
    return new Point();

}

In test class:

Scanner sc = ScannerSingletonKeyboard.getInstance();


int triangleNumber = sc.nextInt();
List<Triangle> triangleList = new ArrayList<Triangle>();
for (int i = 0; i < triangleNumber; i++) {
    Triangle t = new Triangle();
    Triangle t1 = t.readingTriangle(0);
    triangleList.add(t1);

}
System.out.println(triangleList);

and each time you want to use your scanner anywhere you only have to call ScannerSingletonKeyboard.getInstance() for keyboard input or ScannerSingletonFile.getInstance() for file inout which will return your single instance of scanner