Java application doesn't display output

问题

Here's my updated code:

package car1;

public class Main {

public static void main(String[] args) {

class HondaCivic implements car1 {

int speed = 0;
int rpm = 0;
int gear = 1;

public void speedUp(int Increment) {
    speed = speed + Increment;}

public void applyBrakes(int Decrement) {
    speed = speed - Decrement;}

public void changeRpm(int NewValue) {
    rpm = NewValue;}

public void changeGear(int NewValue) {
    gear = NewValue;}

public void printStates() {
    System.out.println("speed:"+speed+" rpm:"+rpm+" gear:"+gear);}

}

class CarDemo{
public void main(String[] args) {
    // Two different Cars
    HondaCivic car1 = new HondaCivic();
    HondaCivic car2 = new HondaCivic();
    // Methods for cars
    car1.speedUp(30);
    car1.changeGear(3);
    car1.changeRpm(3000);
    car1.applyBrakes(15);
    car1.printStates();

    car2.speedUp(30);
    car2.changeGear(3);
    car2.changeRpm(2000);
    car2.applyBrakes(15);
    car2.speedUp(5);
    car2.changeGear(1);
    car2.printStates();
}

} } }

The application will not display the output. I have no idea what to do. Any advice?

回答1:

Java, like most programming languages, is case-sensitive. Class is not the same thing as class.

回答2:

Java is case-sensitive:

Class HondaCivic implements Car {

is not the same as the legal syntax:

class HondaCivic implements Car {

回答3:

An interface needs to implement ALL the methods from its parent. You're implementing everything except for

printStates()

Also, check case sensitivity on your class declaration.

edit: nvm its not declared as abstract

回答4:

You code has many issues.

First make Car an interface like interface Car

Second Move all the code from HondaCivic to Car and all the code from Car to HondaCivic i.e., swap the code because interface can only have method declarations and variables and not implementation. The class implementing the interface needs to provide the implementation of ALL of these methods.

Lastly in the main method write this code instead of what you have for making instances of Car

Car car1 = new HondaCivic();
Car car2 = new HondaCivic();

Then it will compile and run.

回答5:

I can spot several problems, some of which you may have already fixed:

1. Class needs to be class (lowercase) in the second class's definition.
2. Car is not an interface, so you must extend it rather than implement it.
3. HondaCivic is not abstract or an interface, so it must have method bodies for each of its methods; alternatively, leave the methods out of HondaCivic, in which case Car's methods will be used instead.

In your current class layout, it would make much more sense if made a Honda Civic object rather than a class, as it has no new functionality:

Car hondaCivic = new Car();

来源：https://stackoverflow.com/questions/3780594/java-application-doesnt-display-output