Javac “cannot find symbol”

问题:

I've the root directory like this :

├── classes
└── src
    └── vehicles
        ├── Bicycle.java
        └── BicycleMain.java

Bicycle.java

package vehicles;

public class Bicycle {

  public int cadence;
  public int gear;
  public int speed;

  public Bicycle(int startCadence, int startSpeed, int startGear) {
    gear = startGear;
    cadence = startCadence;
    speed = startSpeed;
  }

  public void setCadence(int newValue) {
      cadence = newValue;
  }
  public void setGear(int newValue) {
    gear = newValue;
  }
  public void setSpeed(int newValue) {
    speed = newValue;
  }
  public int getGear() {
    return gear;
  }
  public int getCadence() {
    return cadence;
  }
  public int getSpeed() {
    return speed;
  }
  public void applyBrake(int decrement) {
    speed -= decrement;
  }
  public void speedUp(int increment) {
    speed += increment;
  }

BicycleMain.java

package vehicles; import vehicles.*;

public class BicycleMain {
        public static void main (String args[]){
        Bicycle Bike = new Bicycle(10, 20, 1);
        System.out.println("We have a new bicycle with speed = " +Bike.getSpeed()+", cadence = "+Bike.getCadence()+", gear = "+Bike.getGear());
        } }

I compiled the Bicycle.java and successful, but not for BicycleMain.java :

symbol  : class Bicycle
location: class vehicles.BicycleMain
    Bicycle Bike = new Bicycle(10, 20, 1);
    ^
src/vehicles/BicycleMain.java:6: cannot find symbol
symbol  : class Bicycle
location: class vehicles.BicycleMain
    Bicycle Bike = new Bicycle(10, 20, 1);
                       ^
2 errors

I try to run these files with Netbeans and IT WORKS! but why it doesn't work when I compile in CLI?

回答1:

First, To compile the java source file using javac you need to specify the files to compile explicitly.

Example:

javac PathToSourceFile/FileName.java

you need not provide the path if source file is in current working directory.

Second, whenever java encounters import abc.xyz.ClassName; it tries to resolve abc/xyz/ClassName with respect to the classpath or current working directory.

So if you are inside vehicles folder and compile your code, it wont compile because it will look for folder vehicles inside folder vehicles(which doesn't exists!).

but, you can do this when inside vehicle folder

javac -cp ../ BicycleMain.java

and it should compile, because classpath will be set to directory(../) containing vehicles. which will resolve your Bicycle class.

and then use

java -cp ../ vehicles/BicycleMain to run.

回答2:

Try deleting the line import vehicles.*; from BicycleMain.java and them compiling with javac in command line.

By the way it happens because while you are compiling in javac you are in the folder vehicles and you write a statement import vehicles.*; in BicycleMain.java which means to the compiler there is another folder vehicles within the vehicles folder which is not the case here

回答3:

Just remove the package line from beginning and it'll work 100%.

Go to the folder in which files are stored via terminal and type javac *.java

There will be no need to import classes too.

回答4:

I have solved this problem, compiling from "src".

Something like this: javac ./my_folder/my_file.java

Kind Regards