Java/NetBeans 无法识别主 class 文件之外的常量

Question

I'm working on a project, and trying to do some basic low level things that involve simulated headphones. The class requires three constants for volume, and they are "LOW", "MEDIUM", and "HIGH". The class definition looks like this:

public class HeadPhone {
    public
        static final int LOW = 1;
        static final int MEDIUM = 2;
        static final int HIGH = 3;
    private
        int volume;
        boolean pluggedIn;
        String headPhoneModel;
        String manufacturer;
        Color headPhoneColor; 

Fast forward to my separate test file, and I get the error: "C:\Users\keife\Documents\NetBeansProjects\HeadPhone\src\TestHeadPhone.java:18: error: cannot find symbol HeadPhone Apple = new HeadPhone (LOW, true, "Air Pods", symbol: variable LOW location: class TestHeadPhone". And literally all of my calls that use the variable name of "LOW", "MEDIUM", or "HIGH" are not recognized.

What am I doing wrong? I'm sure my second public declaration is redundant. My default constructor recognizes the variable. I am truly at a loss. Here is my specified constructor, changeVolume() method, creation of new instances of HeadPhones, and referenced setter method just to give any and all relevant code.

    // Specified Constructor, in the main class HeadPhone.java
public HeadPhone (int volume, boolean pluggedIn, 
        String headPhoneModel, String manufacturer,
        Color headPhoneColor) {
    this.volume = volume;
    this.pluggedIn = pluggedIn;
    this.headPhoneModel = headPhoneModel;
    this.manufacturer = manufacturer;
    this.headPhoneColor  = headPhoneColor;
}

// Setter method, explicitly directed to name like this
public void changeVolume (int volume) {
    this.volume = volume;
}
// Create specified HeadPhone, in the test file's main method, TestHeadPHone.java
        HeadPhone Apple = new HeadPhone (LOW, true, "Air Pods", 
                "Apple", Color.white);
        HeadPhone Bose = new HeadPhone (HIGH, true, "Quiet Comfort II",
                "Bose", Color.black);

// Change volume, called from main method in TestHeadPhone.java
        SkullCandy.changeVolume(LOW);
        Apple.changeVolume(MEDIUM);
        Bose.changeVolume(LOW);

Answer 1

First of all, you need to define LOW,MEDIUM,HIGH as public. In java a statement terminates after the semicolon, so in your case only the LOW variable is public. You need to define them as follows:

public static final int LOW = 1;
public static final int MEDIUM = 2;
public static final int HIGH = 3;

Putting public on all variables is not redundant, it is required if you want all of them to be public.

Now in your TestHeadPhone.java you need to import those variables first in order to use them directly like you want to.

It should like something like this, depending on your package name:

import com.package.HeadPhones.LOW;
import com.package.HeadPhones.MEDIUM;
import com.package.HeadPhones.HIGH;

This would allow you to use your public variables by directly using their names without the class name

Or

You could use the variables like so in your constructor call:

// Create specified HeadPhone, in the test file's main method, TestHeadPHone.java
        HeadPhone Apple = new HeadPhone (HeadPhone.LOW, true, "Air Pods", 
                "Apple", Color.white);
        HeadPhone Bose = new HeadPhone (HeadPhone.HIGH, true, "Quiet Comfort II",
                "Bose", Color.black);

Advice

Another advice here, if you want to use values like these, consider using enums.