All classes inherit from java.lang.Object, although extends Object is (generally) not written out anywhere. How is this possible?
所有类都继承自java.lang.Object，尽管extends（通常）不会在任何地方写出。这怎么可能？
2 个解决方案
#1
23
if you don't explicitly write extends Object the compiler does it for you. So knowing that a class can only extend one super class, the compiler will look at the hierarchy and extend the highest super class to Object. So every class will directly or indirectly inherit the Object class.
如果您没有显式编写extends Object，编译器会为您执行此操作。因此，知道一个类只能扩展一个超类，编译器将查看层次结构并将最高的超类扩展为Object。因此每个类都将直接或间接继承Object类。
The Object class however is a special case because it doesn't extend anything.
然而，Object类是一种特殊情况，因为它不会扩展任何东西。
Lastly if you were to compile a simple class and decompile it, you will see the compiler inserts extends java.lang.Object (or the bytecode equivalent) into the class
最后，如果您要编译一个简单的类并对其进行反编译，您将看到编译器将java.lang.Object（或等效的字节码）扩展到类中
#2
5
The Object is implicitly direct/indirect super class of all class.
Object是所有类的隐式直接/间接超类。
From Oracle Java doc:
来自Oracle Java doc：
Definitions: A class that is derived from another class is called a subclass (also a derived class, extended class, or child class). The class from which the subclass is derived is called a superclass (also a base class or a parent class).
定义：从另一个类派生的类称为子类（也是派生类，扩展类或子类）。派生子类的类称为超类（也是基类或父类）。
Excepting Object, which has no superclass, every class has one and only one direct superclass (single inheritance). In the absence of any other explicit superclass, every class is implicitly a subclass of Object.
Excepting Object没有超类，每个类都有一个且只有一个直接超类（单继承）。在没有任何其他显式超类的情况下，每个类都隐式地是Object的子类。
#1
23
if you don't explicitly write extends Object the compiler does it for you. So knowing that a class can only extend one super class, the compiler will look at the hierarchy and extend the highest super class to Object. So every class will directly or indirectly inherit the Object class.
如果您没有显式编写extends Object，编译器会为您执行此操作。因此，知道一个类只能扩展一个超类，编译器将查看层次结构并将最高的超类扩展为Object。因此每个类都将直接或间接继承Object类。
The Object class however is a special case because it doesn't extend anything.
然而，Object类是一种特殊情况，因为它不会扩展任何东西。
Lastly if you were to compile a simple class and decompile it, you will see the compiler inserts extends java.lang.Object (or the bytecode equivalent) into the class
最后，如果您要编译一个简单的类并对其进行反编译，您将看到编译器将java.lang.Object（或等效的字节码）扩展到类中
#2
5
The Object is implicitly direct/indirect super class of all class.
Object是所有类的隐式直接/间接超类。
From Oracle Java doc:
来自Oracle Java doc：
Definitions: A class that is derived from another class is called a subclass (also a derived class, extended class, or child class). The class from which the subclass is derived is called a superclass (also a base class or a parent class).
定义：从另一个类派生的类称为子类（也是派生类，扩展类或子类）。派生子类的类称为超类（也是基类或父类）。
Excepting Object, which has no superclass, every class has one and only one direct superclass (single inheritance). In the absence of any other explicit superclass, every class is implicitly a subclass of Object.
Excepting Object没有超类，每个类都有一个且只有一个直接超类（单继承）。在没有任何其他显式超类的情况下，每个类都隐式地是Object的子类。