Chapter10.statics

BULLET POINTS

A static method should be called using the class name rather than an object reference variable
A static method can be invoked without any instances of the method's class on the heap.
A static method is good for a utility method that does not(and will never) depend on a particular instance variable value.
A static method is not associated with a particular instance--only the class--so it cannot access any instance variable values of its class.It wouldn't know which instance's values to use.
A static method cannot access a non-static method,since non-static methods are usually associated with instance variable state.
If you have a class with only static methods,and you do not want the class to be instantiated,you can mark the constructor private.
A static variable is a variable shared by all members of a given class. There is only one copy of a static variable in a class,rather than one copy per each individual instance for instance variables.
A static method can access a static variable.
To make a constant in Java,mark a variable as both static and final.
A final static variable must be assigned a value either at the time it is declared, or in a static initializer.
```
static {
  DOG_CODE = 420;
}
```
The naming convention for constants(final static variables) is to make the name all uppercase.
A final variable value cannot be changed once it has been assigned.
Assigning a value to a final instance variable must be either at the time it is declared,or in the constructor.
A final method cannot be overridden.
A final class cannot be extended(subclassed).

要点

静态方法应该通过类名调用而不是通过对象引用调用
当堆上没有静态方法的对象实例时，静态方法依然可以被调用。
静态方法是一个好的通用方法，不应该依靠特别的实例变量值。
静态方法与类中的实例变量没有联系，它不能使用类的任何实例变量值。
静态方法不能调用非静态方法。因为非静态方法与实例变量有联系。
如果你的类只有静态方法，并且不希望类被实例化，你可以用private修饰构造函数。
静态变量是可以被类的所有实例共享。静态变量所有类只有一份，而不是每个类的实例各自有一份。
静态方法能使用静态变量。
在Java中创建一个常量，必须使用static和final修饰
一个被final和static修饰的变量必须在声明时或者静态初始化时程序时赋值。
```
static{
  DOG_CODE = 420;
}
```
常量的名字规范是全部大写。
final变量值不能被修改。
final实例变量必须在声明时或者在构造函数中赋值。
final方法不能被覆盖。
final类不能被继承。

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Last updated 6 years ago

BULLET POINTS

A static method should be called using the class name rather than an object reference variable

A static method can be invoked without any instances of the method's class on the heap.

A static method is good for a utility method that does not(and will never) depend on a particular instance variable value.

A static method is not associated with a particular instance--only the class--so it cannot access any instance variable values of its class.It wouldn't know which instance's values to use.

A static method cannot access a non-static method,since non-static methods are usually associated with instance variable state.

If you have a class with only static methods,and you do not want the class to be instantiated,you can mark the constructor private.

A static variable is a variable shared by all members of a given class. There is only one copy of a static variable in a class,rather than one copy per each individual instance for instance variables.

A static method can access a static variable.

To make a constant in Java,mark a variable as both static and final.

A final static variable must be assigned a value either at the time it is declared, or in a static initializer.

static {
  DOG_CODE = 420;
}

The naming convention for constants(final static variables) is to make the name all uppercase.

A final variable value cannot be changed once it has been assigned.

Assigning a value to a final instance variable must be either at the time it is declared,or in the constructor.

A final method cannot be overridden.

A final class cannot be extended(subclassed).

要点

静态方法应该通过类名调用而不是通过对象引用调用

当堆上没有静态方法的对象实例时，静态方法依然可以被调用。

静态方法是一个好的通用方法，不应该依靠特别的实例变量值。

静态方法与类中的实例变量没有联系，它不能使用类的任何实例变量值。

静态方法不能调用非静态方法。因为非静态方法与实例变量有联系。

如果你的类只有静态方法，并且不希望类被实例化，你可以用private修饰构造函数。

静态变量是可以被类的所有实例共享。静态变量所有类只有一份，而不是每个类的实例各自有一份。

静态方法能使用静态变量。

在Java中创建一个常量，必须使用static和final修饰

一个被final和static修饰的变量必须在声明时或者静态初始化时程序时赋值。

static{
  DOG_CODE = 420;
}

常量的名字规范是全部大写。

final变量值不能被修改。

final实例变量必须在声明时或者在构造函数中赋值。

final方法不能被覆盖。

final类不能被继承。