First, the Java Language Foundation (2) _ Types and operations--literals and constants

2018-04-11

Variables and constants

One, constant

　　1. Concept

　　　　　　fixed constant values in the program

2. Classification

　　　1) Literal constants

A direct quantity that represents a direct given value (which can be integers, decimals, ture, false, and so on)

For example: integer value constant, 3.14, 2.25, Boolean constant Ture,false, etc.

　　　2) Final modified variables

Second, the variable

1. Concept

Represents a storage space used to hold constants of a certain type, with no fixed value, can be reused, or can be used to store unknown data of some kind

2. Features

• Occupy a piece of an area in memory
• The zone has its own name (variable name) and type (data type)
• can be reused
• Data in this region can be constantly changed in the same type　　

3 . Defining Variables

1) syntax

Data type variable name

such as: int age;

2) assigning values to variables (initializing)　　

Variable name = constant value of the declared variable type

Age = 17;

You can also initialize variables when declaring variables: int age = 18;

　　Note: variables must be initialized (assigned) before they can be used, and initialization is the true memory allocation.

Iii. Classification of variables-scope-usage rules

　　1. Classification of variables

　　　　Variables fall into two categories depending on the location of the definition

　　　　　1) member variables/fields: variables directly defined in the class {} (outside the method)

2) Environment variables: variables other than member variables, variables defined in the method

　　Note: variable access is the nearest principle

　　2. Scope of variables: areas that can work

1) member variable/field: function in the defined class

2) Environment variables: From the definition of the place to the close immediately after the end of the

Iv. Java expressions

　　

First, the Java Language Foundation (2) _ Types and operations--literals and constants