Do all classes in Java have a parameterless constructor by default?

When there is no constructor defined, each class has a default no-parameter constructor. At this time, the class has only one constructor; and when you explicitly define the constructor of the class, then There is no default constructor. All the constructors of this class are those defined.

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Construction method, as the name suggests, is when you new It is called when an object is created. When there is no constructor defined, each class has a default no-argument constructor. At this time, the class has only one constructor; and when you explicitly define the constructor of the class, there is no default constructor. , all the constructors of this class are those defined; for example: define a Student class:

class Student1｛
//不定义构造方法，此时默认的构造方法是Student1();new
//一个对象时只能这样构造，Student1 s=new Studnet1();
｝
另外再写一个有定义构造方法的类：
class Student2{
Student(String name);
Student(String name,int age);
}

Student2 has two constructors, but there is no default constructor

When creating a Student2 object, you can only use two construction methods

Student2 s2=new Student2("xiaoming");
Student2 s2=new Student2("xiaoqiang",12);

You can also provide more construction methods with any number of parameters. When constructing the object, it is constructed according to the construction method you defined.

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