Why can I not instantiate LocationManager class? [closed]

Question

I am trying to do some work with LocationManager class and saw that I cannot instantiate it.

It is not an abstract class and I was under the impression that only classes marked as abstract could not be instantiated.

Answer 1

For a more complete answer:

If you look at the source code for LocationManager, specifically line 303, you'll see it actually does have a public constructor ... but there's a special annotation:

/**
 * @hide - hide this constructor because it has a parameter
 * of type ILocationManager, which is a system private class. The
 * right way to create an instance of this class is using the
 * factory Context.getSystemService.
 */
public LocationManager(Context context, ILocationManager service) {
    mService = service;
    mContext = context;
}

The @hide annotation keeps the constructor out of the Javadoc and the IDE won't show it. You can read more about the @hide annotation in this SO Q and A

Basically, the class is designed so that you get it from the Context rather than instantiating it yourself. This is a fairly common design for things that require complex (or platform specific) configuration that you want to avoid having the user deal with.

Note that the @hide annotation and its handling are specific to Android.

This is similar to how the Builder or Factory pattern works, where only a builder/factory class can instantiate the object, although usually that's done with a private or package-private constructor in Java:

public class MyWidget
{
    private final Foo someObject; 
    // ... more stuff


    private MyWidget(Builder builder)
    {
        this.someObject = builder.someObject;
        // ... more stuff
    }

    public static class Builder
    {
        Foo someObject;

        public Builder() {}

        public Builder withFoo(Foo someObject)
        {
            this.someObject = someObject;
            return this;
        }

        public MyWidget build()
        {
            return new MyWidget(this);
        }
    }
}

Which gets invoked as:

MyWidget widget = new MyWidget.Builder().withFoo(someFoo).build();