In most object-oriented programming languages such as Java, C++, and C#, you can define multiple constructors each having different signatures. The class calls the correct constructor based on the number of parameters, and data type of input parameters. In PHP5, however, you can have one and only one constructor. Constructor in PHP is defined with a reserved keyword, __construct(). If the __construct function doesn’t exist, PHP5 will search for the old-style constructor function by the name of the class.