What is the default access specifier in Java?

Question

The default visibility is known as “package-private” (though you can't use this explicitly), which means the field will be accessible from inside the same package to which the class belongs.

As mdma pointed out, it isn't true for interface members though, for which the default is "public".

See Java's Access Specifiers

The default specifier depends upon context.

For classes, and interface declarations, the default is package private. This falls between protected and private, allowing only classes in the same package access. (protected is like this, but also allowing access to subclasses outside of the package.)

class MyClass   // package private
{
   int field;    // package private field

   void calc() {  // package private method

   }
}

For interface members (fields and methods), the default access is public. But note that the interface declaration itself defaults to package private.

interface MyInterface  // package private
{
   int field1;         // static final public

   void method1();     // public abstract
}

If we then have the declaration

public interface MyInterface2 extends MyInterface
{

}

Classes using MyInterface2 can then see field1 and method1 from the super interface, because they are public, even though they cannot see the declaration of MyInterface itself.

If no access specifier is given, it's package-level access (there is no explicit specifier for this) for classes and class members. Interface methods are implicitly public.

The default visibility (no keyword) is package which means that it will be available to every class that is located in the same package.

Interesting side note is that protected doesn't limit visibility to the subclasses but also to the other classes in the same package

It depends on what the thing is.

• Top-level types (that is, classes, enums, interfaces, and annotation types not declared inside another type) are package-private by default. (JLS §6.6.1)

• In classes, all members (that means fields, methods, and nested type declarations) and constructors are package-private by default. (JLS §6.6.1)

  • When a class has no explicitly declared constructor, the compiler inserts a default zero-argument constructor which has the same access specifier as the class. (JLS §8.8.9) The default constructor is commonly misstated as always being public, but in rare cases that's not equivalent.

• In enums, constructors are private by default. Indeed, enum contructors must be private, and it is an error to specify them as public or protected. Enum constants are always public, and do not permit any access specifier. Other members of enums are package-private by default. (JLS §8.9)

• In interfaces and annotation types, all members (again, that means fields, methods, and nested type declarations) are public by default. Indeed, members of interfaces and annotation types must be public, and it is an error to specify them as private or protected. (JLS §9.3 to 9.5)

• Local classes are named classes declared inside a method, constructor, or initializer block. They are scoped to the {..} block in which they are declared and do not permit any access specifier. (JLS §14.3) Using reflection, you can instantiate local classes from elsewhere, and they are package-private, although I'm not sure if that detail is in the JLS.

• Anonymous classes are custom classes created with new which specify a class body directly in the expression. (JLS §15.9.5) Their syntax does not permit any access specifier. Using reflection, you can instantiate anonymous classes from elsewhere, and both they and their generated constructors are are package-private, although I'm not sure if that detail is in the JLS.

• Instance and static initializer blocks do not have access specifiers at the language level (JLS §8.6 & 8.7), but static initializer blocks are implemented as a method named <clinit> (JVMS §2.9), so the method must, internally, have some access specifier. I examined classes compiled by javac and by Eclipse's compiler using a hex editor and found that both generate the method as package-private. However, you can't call <clinit>() within the language because the < and > characters are invalid in a method name, and the reflection methods are hardwired to deny its existence, so effectively its access specifier is no access. The method can only be called by the VM, during class initialization. Instance initializer blocks are not compiled as separate methods; their code is copied into each constructor, so they can't be accessed individually, even by reflection.

default is a keyword that is used as an access modifier for methods and variables.
Using this access modifier will make your class, variable, method or constructor acessible from own class or package, it will be also is set if no access modifier is present.

  Access Levels
    Modifier    Class   Package Subclass  EveryWhere
    public        Y        Y       Y         Y
    protected     Y        Y       Y         N
    default       Y        Y       N         N
    private       Y        N       N         N

if you use a default in a interface you will be able to implement a method there like this exemple

public interface Computer {    
    default void Start() {
        throw new UnsupportedOperationException("Error");
    }    
}

However it will only works from the 8 Java version

Official Documentation

Access Modifiers in Java

See here for more details. The default is none of private/public/protected, but a completely different access specification. It's not widely used, and I prefer to be much more specific in my access definitions.