小编use*_*200的帖子

如何检查文件是否存在并打开它？

if(file is found)
{
    FileInputStream file = new FileInputStream("file");
}

Exception in thread "main" java.lang.NullPointerException
    at java.io.Reader.<init>(Unknown Source)
    at java.io.InputStreamReader.<init>(Unknown Source)
//at InputStreamReader inStream = new InputStreamReader(fis);

另外,我应该添加抛出IOException,FileNotFoundException到main还是使用try {}？

    System.out.print("Enter the filename: ");

    Scanner stdin = new Scanner(System.in);  //Keyboard input
    String fileName=stdin.nextLine();

    FileInputStream fis = null;
    try {
        fis = new FileInputStream(fileName);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } 
    InputStreamReader inStream = new InputStreamReader(fis);
    BufferedReader in = new BufferedReader(inStream);

定义objQueue也会得到相同的结果.

public class objQueue extends Vector<Object>
{
...
}

...

objQueue<Customer>[] line=new objQueue<Customer>[num]; //error given on this line

我把它改为公开class objQueue<Object> extends Vector<Object>,但现在它说Cannot create a generic array of objQueue<Customer>.我想定义自己的队列,我应该命名Queue还是其他什么来避免冲突？我正在使用import java.util.*;

如果我将其更改为objQueue<Customer> [] line=new objQueue[num];它会发出警告:类型安全:类型objQueue []的表达式需要未经检查的转换以符合objQueue []