Do constructors always have to be public? [duplicate]

Answer 1

There is no rule that constructor to be public .Generally we define it public just because we would like to instantiate it from other classes too .

Private constructor means,"i dont let anyone create my instance except me ". So normally you would do this when you like to have a singleton pattern.

Following is the class in JDK which uses a private constructor .

public class Runtime {
    private static Runtime currentRuntime = new Runtime();

    public static Runtime getRuntime() {
        return currentRuntime;
    }

    // Don't let anyone else instantiate this class
    private Runtime() {
    }
}