我有一个菜单驱动的程序允许用户在队列中添加、删除和显示一个人的名字。
我的程序编译和运行对我来说是完美的。 但是，当我的讲师测试它时，他说它不会编译并收到此错误？:
QueueProgram.java:24: illegal start of type
MyQueue<String> queue= new MyQueue<>(15);
^
1 error
我的代码:
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import javax.swing.JOptionPane;
public class QueueProgram {
/**
* Driver code to test class
*
* @param arguments
* Commandline arguments not used
* @throws IOException
*/
public static void main(String[] arguments) throws IOException {
//Queue Object
MyQueue<String> queue= new MyQueue<>(15);
String name;
//reading file
read(queue,arguments[0]);
String[] array = { "Offer Person", "Poll Person", "Peek person",
"Display Queue", "Exit Program"};
int choice = 0;
// display loop
while (choice != array.length-1) {
choice = JOptionPane.showOptionDialog(null, // put in center of screen
"Press a Button", // message to user
"Queue(Line) of People", // title of window
JOptionPane.YES_NO_CANCEL_OPTION, // type of option
JOptionPane.QUESTION_MESSAGE, // type of message
null, // icon
array, // array of strings
array[array.length - 1]); // default choice (last one)
if(choice==0){
//inserting the new name in queue
name=JOptionPane.showInputDialog(null,"Enter Person's name","Input");
queue.offer(name);
}
else if(choice==1){
//Display and remove the name which is at front of line
JOptionPane.showMessageDialog(null, queue.poll() + " is next in line");
}
else if(choice==2){
//Display name which is at front of line
JOptionPane.showMessageDialog(null, queue.peek() + " is front of the line");
}
else if(choice==3){
//Dispay all the list
JOptionPane.showMessageDialog(null, queue.toString());
}
//JOptionPane.showMessageDialog(null, "Your pressed button #" + choice);
}
//calling writing function
write(queue, arguments[1]);
}// end of main()
/**
* Reads a file
* @param queue
* @param file_name name of file
*/
public static void read(QueueInterface<String> queue, String file_name) throws IOException{
String name;
//creating a buffer reader to read
BufferedReader br= new BufferedReader(new FileReader(file_name));
while((name=br.readLine()) != null){
//putting in the queue
queue.offer(name);
}
//closing buffer reader
br.close();
}
/**
* Writes to file
* @param queue QueueInterface methods
* @param file_name name of file
*/
public static void write(QueueInterface<String> queue, String file_name) throws IOException{
String name;
//creating a buffer writer to write
BufferedWriter bw= new BufferedWriter(new FileWriter(file_name));
while((name=queue.poll()) != null){
//writin in file
bw.write(name);
bw.newLine();
}
//closing buffer
bw.close();
}
}// end of class
class MyQueue<T> extends ArrayQueue<T>{
/**
* Constructor
*
* @param max is the greatest number of elements in the queue
*/
public MyQueue(int max) {
super(max);
}
/**
* Returns a string representation of the object
*
* @return a name on different lines
*/
public String toString() {
// create a variable
String element = "";
int count=frontIndex;
// check to see if not empty
if (!this.empty()) {
// get the address of front element
while(count<=endIndex){
element = element +(String) array[count]+"\n";
count++;
}
}
// return either null or element
return element;
}
}
知道是什么导致了这个错误吗？
最佳答案
菱形运算符 ( <> ) 仅在 Java 7 中引入。您应该明确指定类型参数 ( new MyQueue<String>(15) )，您的教师将能够对其进行编译。
您可以在此处找到解释 - Java SE 7 Features and Enhancements - Type Inference for Generic Instance Creation .
关于java - Java 类型的非法开始，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22826547/