程序编译并运行，但不输出任何内容

Question

I've never had this issue and since there are no errors given, I am unsure of where to even look. I've had a heck of a time with this program (it is my first time doing methods). Prior to this issue, it kept throwing exceptions. While I researched that piece, and managed to fix the error, I get the feeling it isn't right. Please let me know if the entire code is off (preferably some constructive criticism) or if I'm close:

import java.io.*;

public class InsuranceMethod2//class name here, same as file name

{   

// use BufferedReader class to input from the keyboard
// declare a variable of type BufferedReader
private BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
//declare variable for input
private String inputString;

    String carChoice;
    boolean insurable;
    int year;

public void InsuranceMethod2()throws IOException{//constructor, place class name here

String carChoice;
boolean insurable;
int year; 

initialize();
insureProcess();
cleanUp();
}//end constructor

public void initialize(){
    System.out.println();
    System.out.println("Insurance Process Intializing");
}//end initialize

public void insureProcess() throws IOException {

    String carChoice;
    boolean insurable;
    int year;

    System.out.println("Enter your vehicle model: ");
    inputString = input.readLine();
    carChoice = inputString;
            if(carChoice.equalsIgnoreCase("ford") || carChoice.equalsIgnoreCase("chevy") || carChoice.equalsIgnoreCase("toyota"))
    {
        System.out.println("Enter the vehicle year: ");
        inputString = input.readLine();
        year = Integer.parseInt(inputString);
        if(year >= 1990)
        {
            System.out.println("Your vehicle is insurable");
        }
    }
}

public boolean checkModel(){
    if(carChoice.equalsIgnoreCase("Ford")|| carChoice.equalsIgnoreCase("Chevy")|| carChoice.equalsIgnoreCase("Toyota"))
    {
        return true;
    }
    else
    {
        return false;
    }
}//end checkModel

public boolean checkYear(int year){
    return false;
}//end checkYear

public void printResults(boolean insurable){

}//end printResults

public void cleanUp(){
    System.out.println("Program ending");
}//end cleanUp

public static void main(String [] args) throws IOException // main method

{
    new InsuranceMethod2(); //class constructor name
} // end the main method
} // end the program

Answer 1

 public void InsuranceMethod2() throws IOException{ //constructor

That is not a constructor. It's just a method (with a very confusing name).

You want

 public InsuranceMethod2() throws IOException{ //constructor

Without that, you just get a default constructor that does nothing.

You should also make all methods called from a constructor private or at least final.

Answer 2

The only thing your program does is create a new instance of the InsuranceMethod class. This class's constructor then runs, and since you haven't defined one (your defined method has a return type which makes it not a constructor), the default constructor runs (and does nothing). Therefore, you are seeing no output. If you wish to call the method by the same name, write:

new InsuranceMethod2().InsuranceMethod2();

Otherwise you should remove the void keyword from your method to turn it into a constructor.

Answer 3

public void InsuranceMethod2()throws IOException{//constructor, place class name here

The code above is not a constructor, as it is a method declaration. If you want it to be a constructor, remove the void , so it will look something like this:

public InsuranceMethod2() throws IOException{ ... }

Also, you have already globally declared your variables, there is no need to keep declaring them again in each method because when you try referencing that variable, it will reference the locally declared variable as opposed to the globally declared variable, so you will receive unexpected results.

As a tip though, if you have field names that are common within your global variable declarations and your local variable declarations, you can reference the global variable by suffixing a this. before it.

Answer 4

There seems to be a few misconceptions within your code. To answer your direct question, a constructor doesn't have a return type (see this tutorial ). So simply change your constructor (which in your case is actually a method) to

public InsuranceMethod2() throws IOException{ ... }

To address the other misconceptions (where to declare variables, styling, etc.), I rewrote your code a bit with comments (look for LEBOLO). For details on styling, it's best to just Google "java code style" or "java code conventions". I hope this helps and points you towards more learning resources! Have fun!

Rewritten Code

import java.io.*;

public class InsuranceMethod2 { //class name here, same as file name   

    // use BufferedReader class to input from the keyboard
    // declare a variable of type BufferedReader
    private BufferedReader input = new BufferedReader( new InputStreamReader(System.in) );

    // declare variable for input
    //private String inputString; // LEBOLO: Remove, don't need (see larger comment below for details)

    /* LEBOLO
     *
     * Do you want all of these as class level variables? I assume you don't since you don't use them all.
     * In general, you only put variables here (called instance variables) if you want multiple methods to share them.
     * You don't have to declare variables here just because one method uses them.
     * See http://docs.oracle.com/javase/tutorial/java/javaOO/variables.html for details.
     *
     * Also, by not stating a modifier (e.g. private or public), Java defaults to the package access level.
     * See http://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html for details
     */
    String carChoice; // LEBOLO: I think you want this private
    //boolean insurable; // LEBOLO: Remove, don't need
    //int year; // LEBOLO: Remove, don't need

    // LEBOLO: Removed the void return type.
    // See http://docs.oracle.com/javase/tutorial/java/javaOO/constructors.html for details.
    public InsuranceMethod2() throws IOException { // constructor, place class name here

        //String carChoice; // LEBOLO: Remove, don't need
        //boolean insurable; // LEBOLO: Remove, don't need
        //int year; // LEBOLO: Remove, don't need

        initialize();
        insureProcess();
        cleanUp();
    } // end constructor

    public void initialize() {
        System.out.println();
        System.out.println("Insurance Process Intializing");
    } // end initialize

    public void insureProcess() throws IOException {

        /* LEBOLO
         *
         * Since you use the 'year' variables here, it makes sense to declare it here (local variables).
         * You don't use 'insurable' and 'carChoice' is an instance (class level) variable, so no need to declare here.
         */

        //String carChoice; // LEBOLO: Remove, don't need (since using the instance variable)
        //boolean insurable; // LEBOLO: Remove, don't need
        int year;

        System.out.println("Enter your vehicle model: ");

        // LEBOLO: Declare inputString here, since you only use it here
        String inputString = input.readLine();
        carChoice = inputString;

        if (carChoice.equalsIgnoreCase("ford") || carChoice.equalsIgnoreCase("chevy") || carChoice.equalsIgnoreCase("toyota")) {
            System.out.println("Enter the vehicle year: ");
            inputString = input.readLine();

            year = Integer.parseInt(inputString);
            if (year >= 1990) {
                System.out.println("Your vehicle is insurable");
            }
        }
    }

    public boolean checkModel() {

        if(carChoice.equalsIgnoreCase("Ford")|| carChoice.equalsIgnoreCase("Chevy")|| carChoice.equalsIgnoreCase("Toyota")) {
            return true;
        }
        else
        {
            return false;
        }

        /* LEBOLO: A cleverer way would be
         *
         * return (carChoice.equalsIgnoreCase("Ford")|| carChoice.equalsIgnoreCase("Chevy")|| carChoice.equalsIgnoreCase("Toyota"));
         */
    }//end checkModel

    /* LEBOLO
     *
     * If you want to use the shared year, then declare the variable at the class level (instance variable)
     * and remove it from the method signature (instead using it within the method body).
     *
     * public boolean checkYear() {
     *     return (year >= 1990);
     * } // end checkYear
     *
     * If you want the user to say checkYear(1993), then leave this as is.
     */
    public boolean checkYear(int year) {
        return false;
    } // end checkYear

    /* LEBOLO
     * 
     * See my comment for checkYear(...)
     */
    public void printResults(boolean insurable) {
    } // end printResults

    public void cleanUp() {
        System.out.println("Program ending");
    } // end cleanUp

    public static void main(String [] args) throws IOException { // main method
        new InsuranceMethod2(); // class constructor name
    } // end the main method
} // end the program