Why am I getting an Unreachable Statement error in

问题:

When I try to compile this program, I get an "unreachable statement" error in line 21:

import java.util.*;
import java.io.*;
import java.nio.file.*;
import java.lang.StringBuilder;

class FilePrep {
    public static void main(String args[]) {
    }
    public String getStringFromBuffer() {
        try {
            Path file = Paths.get("testfile2.txt");
            FileInputStream fstream = new FileInputStream("testfile2.txt");
            BufferedReader br = new BufferedReader(new InputStreamReader(fstream));  
                String inputLine = null;                    
            StringBuffer theText = new StringBuffer();  

            while((inputLine=br.readLine())!=null) {
                theText.append(inputLine+" ");
            }
            return theText.toString();
            System.out.println(theText); // <-- line 21
        }
        catch (Exception e)
        {
            System.err.println("Error: " + e.getMessage());
            return null;
        }
    }
}

The full compiler output is:

Main.java:21: error: unreachable statement
            System.out.println(theText);
            ^
Main.java:28: error: missing return statement
    }
    ^
2 errors

I think the return statements are in the right places...they seem to be to me at least, and the program seems so simple compared to the one that I cloned it from, that I'm having a really hard time figuring out why this statement is unreachable.

What did I do wrong while copying the code, and how do I need to correct it?

回答1:

You were right assuming that your problem is here:

return theText.toString();
System.out.println(theText);

the return function will terminate your method, meaning no line of code past it will be executed. If you want your print to go through, you should move it above the return statement.

回答2:

You've got a statement after the return statement. Here's the two offending lines:

return theText.toString();
System.out.println(theText);

Switch them around.

System.out.println(theText);
return theText.toString();

回答3:

When the return statement is executed, the method relinquish control to its caller. That is why the println will not run; that's why the compiler complains.

Unreachable statements are certain and reliable indicators of a logical error in your program. It means that you put in statements that will not be executed, but you assume that they would be. The compiler analyzes the flow, and reports these statements to you as error messages.

回答4:

The print statement comes after a return statement. The function will always exit before it gets to the print statement. "Unreachable"

        return theText.toString(); 
        System.out.println(theText); 

Switch the order of the two lines around and it will work.

回答5:

The return statement always should be at the end or last line of the definition block. If you keep any statements after the return statement those statements are unreachable statements by the controller. By using return statement we are telling control should go back to its caller explicitly.

For example

public class Z
{
    public int test()
    {
        System.out.println(10);
        return 10;
        System.out.println(20);
    }
}

In this example we get compile time error as unreachable code because control cannot reach to last statement for execution.

So, always return statement should be the last statement of a definition block.