Constructors in Java are special methods used to initialize objects when they are created. Their name must match the class name exactly and they do not have a return type. Constructors can accept parameters to initialize objects with specific values during creation. If a class does not explicitly define a constructor, the Java compiler automatically provides a default no-argument constructor. However, if a constructor is defined in the class, the default constructor is not generated. Constructors can be overloaded, meaning a class can have multiple constructors as long as their parameter lists differ.