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:
class Person //人类{ public Person(String n,int a) //构造方法 { name = n; age = a; } private string name; private int age; } static void main(String[] args){ Person p = new Person("张三",14);//这就是作用,为其初始化 }
Constructor is used when new an object,
For example:
Hello hello = new Hello();//这时调用的是Hello的无参数构造方法; Hello hello = new Hello("hi");//这个是调用Hello有参数构造方法,
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.
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