请解释一下这种情况：扫描仪在继承

我创建了2类：四合院和点，四合院使用4个点创建一个实例。请解释一下这种情况：扫描仪在继承

在点，我有一个扫描仪得到inputPoint，这样我就可以用这些点数来建立一个四合院

的更详细的实施在下面的源代码提供。问题是，

当我做了扫描仪的inputPoint内部本地，它需要在方法的端部紧密权利。

如果我关闭它，inputQuadrangle方法中的inputPoint不能连续使用以创建4个需要的点。我只是认为，在每个inputPoint调用时，扫描器一次又一次地创建，它应该可以工作。那么，这里有什么问题？

下面的代码块中存在错误。

如果我不关闭它，在Point类中存在一个弱点，但inputQuadrangle方法中的inputPoint可以连续使用以创建4个需要的点。
但是，当我使扫描仪静态像一个字段，它不需要关闭，并与此同时，我可以在inputQuadrangle方法中使用inputPoint没有任何错误或弱点。

那么，我错过了什么？请指出。

Point class with local scanner 
package OOPBaiTap; 

import java.util.Scanner; 

public class Point { 
// Thuoc tinh 
private String name; 
private double x; 
private double y; 

// Phuong thuc khoi tao mac dinh 
public Point() { 
    this("A", 0, 0); 
} 

// Phuong thuc khoi tao nhan hai so thuc lam tham so 
public Point(double x, double y) { 
    this.x = x; 
    this.y = y; 
} 

// Phuong thuc khoi tao nhan mot chuoi va hai so thuc lam tham so 
public Point(String name, double x, double y) { 
    this.name = name; 
    this.x = x; 
    this.y = y; 
} 

// Phuong thuc khoi toa nhan mot doi tuong cua lop Poin lam tham so 
public Point(Point point) { 
    this.name = point.getName(); 
    this.x = point.getX(); 
    this.y = point.getY(); 
} 

// Cac phuong thuc get, set 
public String getName() { 
    return name; 
} 

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

public double getX() { 
    return x; 
} 

public void setX(double x) { 
    this.x = x; 
} 

public double getY() { 
    return y; 
} 

public void setY(double y) { 
    this.y = y; 
} 

// Phuong thuc nhap vao mot diem duoi dang hai so thuc, cach nhau boi dau 
// "," 
public static Point inputPoint() { 
    Point point = null; 
    System.out 
      .println("Nhap vao tung do va hoanh do, cach nhau mot khoang trang: "); 
    Scanner input = new Scanner(System.in); 
    String[] s = input.nextLine().split(" "); 
    point = new Point(Double.parseDouble(s[0]), Double.parseDouble(s[1])); 
    input.close(); 
    return point; 
} 

// Phuong thuc toString() 
@Override 
public String toString() { 
    String s; 
    if (this.getName() != null) { 
     s = this.getName() + "(" + this.getX() + ", " + this.getY() + ")"; 
    } else { 
     s = "(" + this.getX() + ", " + this.getY() + ")"; 
    } 
    return s; 
} 

// Phuong thuc main 
public static void main(String[] args) { 
    // Diem khoi tao mac dinh 
    Point A = new Point(); 
    System.out.println(A.toString()); 
    System.out.println(); 
    // Diem khoi tao voi hai so thuc 
    Point B = new Point(2, 5); 
    System.out.println(B.toString()); 
    System.out.println(); 
    // Diem khoi tao voi mot xau va hai so thuc 
    Point C = new Point("C", 4, 5); 
    System.out.println(C.toString()); 
    Point D = new Point("D", 3, 2); 
    System.out.println(); 
    // Diem khoi tao voi tham so la mot doi tuong cua lop Point 
    Point E = new Point(D); 
    System.out.println(E.toString()); 
    System.out.println(); 
    // Nhap vao tung do va hoanh do cua mot diem, sau do in diem do ra 
    // console 
    Point F = inputPoint(); 
    System.out.println(F.toString()); 
} 
}

Error code thrown out when trying to input a Quadrangle. 
**** 

input p1: success 

input p2: 

Exception in thread "main" Java.util.NoSuchElementException: No line found 

at Java.util.Scanner.nextLine(Scanner.Java:1540) 

at OOPBaiTap.Point.inputPoint(Point.Java:68) 

at OOPBaiTap.Quadrangle.inputQuadrangle(Quadrangle.Java:30) 

at OOPBaiTap.Quadrangle.main(Quadrangle.Java:95)

Point class with static field scanner 
package OOPBaiTap; 

import java.util.Scanner; 

public class Point { 
// Thuoc tinh 
private String name; 
private double x; 
private double y; 
private static Scanner input; 

// Phuong thuc khoi tao mac dinh 
public Point() { 
    this("A", 0, 0); 
} 

// Phuong thuc khoi tao nhan hai so thuc lam tham so 
public Point(double x, double y) { 
    this.x = x; 
    this.y = y; 
} 

// Phuong thuc khoi tao nhan mot chuoi va hai so thuc lam tham so 
public Point(String name, double x, double y) { 
    this.name = name; 
    this.x = x; 
    this.y = y; 
} 

// Phuong thuc khoi toa nhan mot doi tuong cua lop Poin lam tham so 
public Point(Point point) { 
    this.name = point.getName(); 
    this.x = point.getX(); 
    this.y = point.getY(); 
} 

// Cac phuong thuc get, set 
public String getName() { 
    return name; 
} 

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

public double getX() { 
    return x; 
} 

public void setX(double x) { 
    this.x = x; 
} 

public double getY() { 
    return y; 
} 

public void setY(double y) { 
    this.y = y; 
} 

// Phuong thuc nhap vao mot diem duoi dang hai so thuc, cach nhau boi dau 
// "," 
public static Point inputPoint() { 
    Point point = null; 
    System.out 
      .println("Nhap vao tung do va hoanh do, cach nhau mot khoang trang: "); 
    input = new Scanner(System.in); 
    String[] s = input.nextLine().split(" "); 
    point = new Point(Double.parseDouble(s[0]), Double.parseDouble(s[1])); 
    return point; 
} 

// Phuong thuc toString() 
@Override 
public String toString() { 
    String s; 
    if (this.getName() != null) { 
     s = this.getName() + "(" + this.getX() + ", " + this.getY() + ")"; 
    } else { 
     s = "(" + this.getX() + ", " + this.getY() + ")"; 
    } 
    return s; 
} 

// Phuong thuc main 
public static void main(String[] args) { 
    // Diem khoi tao mac dinh 
    Point A = new Point(); 
    System.out.println(A.toString()); 
    System.out.println(); 
    // Diem khoi tao voi hai so thuc 
    Point B = new Point(2, 5); 
    System.out.println(B.toString()); 
    System.out.println(); 
    // Diem khoi tao voi mot xau va hai so thuc 
    Point C = new Point("C", 4, 5); 
    System.out.println(C.toString()); 
    Point D = new Point("D", 3, 2); 
    System.out.println(); 
    // Diem khoi tao voi tham so la mot doi tuong cua lop Point 
    Point E = new Point(D); 
    System.out.println(E.toString()); 
    System.out.println(); 
    // Nhap vao tung do va hoanh do cua mot diem, sau do in diem do ra 
    // console 
    Point F = inputPoint(); 
    System.out.println(F.toString()); 
} 
}

Quadrangle class 
package OOPBaiTap; 

public class Quadrangle { 
// Thuoc tinh 
private Point p1; 
private Point p2; 
private Point p3; 
private Point p4; 

// Phuong thuc khoi tao mac dinh 
public Quadrangle() { 
    this(new Point("A", 0, 0), new Point("B", 0, 1), new Point("C", 1, 1), 
      new Point("D", 1, 0)); 
} 

// Phuong thuc khoi tao nhan 4 doi tuong thuoc lop poin lam tham so 
public Quadrangle(Point p1, Point p2, Point p3, Point p4) { 
    this.p1 = p1; 
    this.p2 = p2; 
    this.p3 = p3; 
    this.p4 = p4; 
} 

// Phuong thuc nhap vao mot tu giac 4 diem tu ban phim 
public static Quadrangle inputQuadrangle() { 
    Quadrangle quadrangle = null; 
    System.out.println("Nhap vao diem p1: "); 
    Point p1 = Point.inputPoint(); 
    System.out.println("Nhap vao diem p2: "); 
    Point p2 = Point.inputPoint(); 
    System.out.println("Nhap vao diem p3: "); 
    Point p3 = Point.inputPoint(); 
    System.out.println("Nhap vao diem p4: "); 
    Point p4 = Point.inputPoint(); 
    quadrangle = new Quadrangle(p1, p2, p3, p4); 
    return quadrangle; 
} 

// Cac phuong thuc get set 
public Point getP1() { 
    return p1; 
} 

public void setP1(Point p1) { 
    this.p1 = p1; 
} 

public Point getP2() { 
    return p2; 
} 

public void setP2(Point p2) { 
    this.p2 = p2; 
} 

public Point getP3() { 
    return p3; 
} 

public void setP3(Point p3) { 
    this.p3 = p3; 
} 

public Point getP4() { 
    return p4; 
} 

    public void setP4(Point p4) { 
    this.p4 = p4; 
} 

// Phuong thuc toString() 
@Override 
public String toString() { 
    String s = new String(p1.toString() + ", " + p2.toString() + ", " 
      + p3.toString() + ", " + p4.toString() + "."); 
    return s; 
} 

// Phuong thuc main() 
public static void main(String[] args) { 
    // Phuong thuc khoi tao mac dinh 
    Quadrangle a = new Quadrangle(); 
    System.out.println(a.toString()); 
    System.out.println(); 
    // Phuong thuc khoi tao nhan 4 doi tuong thuoc lop point lam tham so 
    Point p1 = new Point(0, 0); 
    Point p2 = new Point(0, 2); 
    Point p3 = new Point(2, 1); 
    Point p4 = new Point(1, 0); 
    Quadrangle b = new Quadrangle(p1, p2, p3, p4); 
    System.out.println(b.toString()); 
    System.out.println(); 
    // Nhap vao 4 diem cua tu giac tu ban phim 
    Quadrangle c = inputQuadrangle(); 
    System.out.println(c.toString()); 
} 
}

来源

2014-10-05 luan

关闭'java.util.Scanner'（使用'input.close（）'）还会关闭基础流'System.in'。后续对'Scanner.nextLine（）'的调用无法从关闭的System.in中读取更多行。 – halfbit 2014-10-05 10:36:38

这是从文档System.in

The "standard" input stream. This stream is already open and ready to supply input data. 
Typically this stream corresponds to keyboard input or another input source specified by 
the host environment or user.

所以，你不必担心关闭System.in，因为它有主要为debugging/testing目的（S）和关闭一次，你不应该尝试阅读从这将导致例外。

您正在获得NoSuchElementException例外，因为System.in是closed在先前调用inputPoint()时您的代码正在尝试从中读取。另外，错误与static无关，正如您在第二点中引用的那样。在这种情况下，如果关闭扫描器实例，您也会得到相同的错误。

但是，如果它指向某个系统资源（如file）的流应关闭它。

来源

2014-10-05 10:47:42 Tirath

非常感谢。我知道了。我绝对是Java新手:) – luan 2014-10-05 13:15:33

请解释一下这种情况：扫描仪在继承

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