Language Fundamentals - Constructor Declarations

Syntax (JLS §8.8)

        modifiers ClassName(arguments) throwsClause {
            // Constructor body
        }

The modifers, ClassName, arguments, and throwsClause are optional.

[Note: all are optional in the sense that your class does NOT have to declare a constructor (see following on default constructors);however, if you do include a constructor modifiers, arguments and the throws clause are optional.]

• a constructor can use the access modifiers public, protected or private or have no access modifier (package access)
• a constructor can not use the modifiers abstract, static, final, native, synchronized or strictfp (JLS §8.8.3)
• constructors are not considered class members, they are not inherited
• if a class constructor is not declared, a default constructor is supplied by the compiler

          modifiers ClassName() {
              super();                
          }
  

• the default constructor has the same access modifier as the class itself, either: public, protected, private or package (no modifier)
• to prevent a class from being instantiated outside the class declaration you can create a private constructor.

    public void MyClassName() {}    // not a constructor
    public MyClassName() {}         // constructor

Tips

• a constructor body can include a return statement providing no value is returned

Traps

• subclass with default constructor when the superclass does not have a no-args constructor or it's no-arg constructor has a throws clause
• constructor declared with a return type