The function of the constructor method is to initialize the class. If you do not agree on the form of any constructor, the program will take a constructor without any parameters for you. Then you can only use the method without parameters when generating a class object, such as: class a {}// There isn't any constructor.

The name of the constructor must be the same as the class name, including upper and lower case;

The constructor has no return value and cannot be modified with void. If you are not careful Adding a return value type in front of the constructor will turn the constructor into an ordinary method, and an error that the constructor cannot be found will be generated at runtime.

A class can define multiple constructors. If no constructor is defined when defining a class, the compilation system will automatically insert a parameterless default constructor, which does not execute any code.

Constructor methods can be overloaded according to the number, type, and order of parameters.

Examples are as follows:

Constructor is used when new an object,

For example:

In JAVA, if you do not write a constructor, a parameterless constructor will be added by default. However, if there is already a parameterized constructor, the parameterless constructor will not be added by default. .

If the Hello class already has a constructor with parameters, then an error will occur when using Hello hello = new Hello(); to create an object. This is why the book emphasizes writing If you have a parameterized constructor, it is best to add a parameterless constructor.

The above is the detailed content of What is the constructor method in java. For more information, please follow other related articles on the PHP Chinese website!