請解釋一下這種情況：掃描儀在繼承

我創建了2類：四合院和點，四合院使用4個點創建一個實例。請解釋一下這種情況：掃描儀在繼承

在點，我有一個掃描儀得到inputPoint，這樣我就可以用這些點數來建立一個四合院

的更詳細的實施在下面的源代碼提供。問題是，

當我做了掃描儀的inputPoint內部本地，它需要在方法的端部緊密權利。

如果我關閉它，inputQuadrangle方法中的inputPoint不能連續使用以創建4個需要的點。我只是認爲，在每個inputPoint調用時，掃描器一次又一次地創建，它應該可以工作。那麼，這裏有什麼問題？

下面的代碼塊中存在錯誤。

如果我不關閉它，在Point類中存在一個弱點，但inputQuadrangle方法中的inputPoint可以連續使用以創建4個需要的點。
但是，當我使掃描儀靜態像一個字段，它不需要關閉，並與此同時，我可以在inputQuadrangle方法中使用inputPoint沒有任何錯誤或弱點。

那麼，我錯過了什麼？請指出。

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()); 
} 
}

來源

2014-10-05 luan

關閉'java.util.Scanner'（使用'input.close（）'）還會關閉基礎流'System.in'。後續對'Scanner.nextLine（）'的調用無法從關閉的System.in中讀取更多行。 – halfbit 2014-10-05 10:36:38

這是從文檔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，你不必擔心關閉System.in，因爲它有主要爲debugging/testing目的（S）和關閉一次，你不應該嘗試閱讀從這將導致例外。

您正在獲得NoSuchElementException例外，因爲System.in是closed在先前調用inputPoint()時您的代碼正在嘗試從中讀取。另外，錯誤與static無關，正如您在第二點中引用的那樣。在這種情況下，如果關閉掃描器實例，您也會得到相同的錯誤。

但是，如果它指向某個系統資源（如file）的流應關閉它。

來源

2014-10-05 10:47:42 Tirath

非常感謝。我知道了。我絕對是Java新手:) – luan 2014-10-05 13:15:33

請解釋一下這種情況：掃描儀在繼承

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