扫描器抛出 InputMismatchException 为 null
Scanner throws InputMismatchException with null
import java.io.*;
import java.util.*;
public class Main{
public static void main(String [] args) throws InputMismatchException{
double width;
int period;
double Ppp;
Scanner in0 = new Scanner(System.in);
Scanner in1 = new Scanner(System.in);
Scanner in2 = new Scanner(System.in);
System.out.println("Give width\n");
while(in0.hasNextDouble()){
width = in0.nextDouble();
}
in0.close();
System.out.println("\n");
System.out.println("Give period");
while(in1.hasNextInt()){
period = in1.nextInt();
}
in1.close();
System.out.println("\n");
System.out.println("Insert width peak to peak");
while(in2.hasNextDouble()){
Ppp = in2.nextDouble();
}
in2.close();
}
我运行这个代码块
我插入第一个输入,但它为每个输入显示 null
然后它崩溃了
让某人 运行 告诉他是否有同样的问题
我使用 BlueJ 编译器
public static void main(String [] args) throws InputMismatchException{
double width;
int period;
double Ppp;
Scanner in0 = new Scanner(System.in);
System.out.println("Give width\n");
// This will read the line, and parse the result as a double, this way you can insert a number and press enter
width = Double.parseDouble(in0.nextLine());
System.out.println("Give period");
period = Integer.parseInt(in0.nextLine());
System.out.println("\n");
System.out.println("Insert width peak to peak:");
ppp = Double.parseDouble(in0.nextLine());
in0.close();
}
问题的原因是这个
Scanner in0 = new Scanner(System.in);
Scanner in1 = new Scanner(System.in);
Scanner in2 = new Scanner(System.in);
还有这个
in0.close();
...
in1.close();
...
in2.close();
创建扫描仪时,您会处理 System.in
,然后关闭它。这导致下一个扫描器在关闭的流上运行。
解决方案是为 InputStream
创建一个 Scanner
。
Scanner scanner = new Scanner(System.in);
System.out.println("Give width\n");
double width = scanner.nextDouble();
System.out.println("Give period");
int period = scanner.nextInt();
System.out.println("\nInsert width peak to peak:");
double p2p = scanner.nextDouble();
这只是不验证用户输入的示例。
import java.io.*;
import java.util.*;
public class Main{
public static void main(String [] args) throws InputMismatchException{
double width;
int period;
double Ppp;
Scanner in0 = new Scanner(System.in);
Scanner in1 = new Scanner(System.in);
Scanner in2 = new Scanner(System.in);
System.out.println("Give width\n");
while(in0.hasNextDouble()){
width = in0.nextDouble();
}
in0.close();
System.out.println("\n");
System.out.println("Give period");
while(in1.hasNextInt()){
period = in1.nextInt();
}
in1.close();
System.out.println("\n");
System.out.println("Insert width peak to peak");
while(in2.hasNextDouble()){
Ppp = in2.nextDouble();
}
in2.close();
}
我运行这个代码块 我插入第一个输入,但它为每个输入显示 null 然后它崩溃了 让某人 运行 告诉他是否有同样的问题 我使用 BlueJ 编译器
public static void main(String [] args) throws InputMismatchException{
double width;
int period;
double Ppp;
Scanner in0 = new Scanner(System.in);
System.out.println("Give width\n");
// This will read the line, and parse the result as a double, this way you can insert a number and press enter
width = Double.parseDouble(in0.nextLine());
System.out.println("Give period");
period = Integer.parseInt(in0.nextLine());
System.out.println("\n");
System.out.println("Insert width peak to peak:");
ppp = Double.parseDouble(in0.nextLine());
in0.close();
}
问题的原因是这个
Scanner in0 = new Scanner(System.in);
Scanner in1 = new Scanner(System.in);
Scanner in2 = new Scanner(System.in);
还有这个
in0.close();
...
in1.close();
...
in2.close();
创建扫描仪时,您会处理 System.in
,然后关闭它。这导致下一个扫描器在关闭的流上运行。
解决方案是为 InputStream
创建一个 Scanner
。
Scanner scanner = new Scanner(System.in);
System.out.println("Give width\n");
double width = scanner.nextDouble();
System.out.println("Give period");
int period = scanner.nextInt();
System.out.println("\nInsert width peak to peak:");
double p2p = scanner.nextDouble();
这只是不验证用户输入的示例。