Keywords and identifiers
Use the keyword 1.java
Definition: The Java language is given a special meaning, with special purposes string (word)
Features: keywords are lowercase letters
exactly which keywords:
2. Reserved words : now Java version has not been used, but later versions may use as keywords.
What specific reserved words: goto, const
Note: When naming their own identifier to avoid using these reserved words
3. Use of identifiers
defined: those who own place from the name of the call identifier.
Related to the structure:
the package name, class name, interface name, variable names, method names, constant names,
rules must be observed :( Otherwise, the compiler does not pass).
:( can not comply with specifications, does not affect compile and run, but ask you to follow )
Note the point:
when a name in order to improve readability, as far as possible sense, "see the name to know Italian."
Use variables
1.1 by data type
Detailed Description:
1. Integer: byte (byte. 1 = 8bit) \ short (2 bytes) \ int (4 bytes) \ long (. 8 bytes)
① byte range: -128 ~ 127
② long variable declarations , must be "l" or "L" end
③ typically, the definition of an integer variable, using an int.
④ integer constant, the default type is: int type
2. Float : float (4 bytes) \ double (8 bytes)
① float, a numerical value with decimal
② float represents a range of values larger than the long
time ③ defined float type variables, variables to " f "or" F "end
④ typically, when the float variable is defined, using double.
⑤ floating-point constants, default type is: double
3. Character : char (2 bytes = 1 character)
① char type variable is defined, a pair of generally '', only the internal write a character
② representation: 1. Declare a character escape character 2. 3. Direct use Unicode character values to represent constants
4 Boolean: Boolean
① can only take one of two values: to true, to false
② often conditional, loop structure used
1.2 Classification of statement by location
2. The definition of a variable format:
Data type variable name = variable value;
or
data type variable name;
variable name = variable value;
3.变量使用的注意点：
① 变量必须先声明，后使用
② 变量都定义在其作用域内。在作用域内，它是有效的。换句话说，出了作用域，就失效了
③ 同一个作用域内，不可以声明两个同名的变量
4.基本数据类型变量间运算规则
4.1 涉及到的基本数据类型：除了boolean之外的其他7种
4.2 自动类型转换(只涉及7种基本数据类型）
结论：当容量小的数据类型的变量与容量大的数据类型的变量做运算时，结果自动提升为容量大的数据类型。
byte 、char 、short --> int --> long --> float --> double
特别的：当byte、char、short三种类型的变量做运算时，结果为int型
说明：此时的容量大小指的是，表示数的范围的大和小。比如：float容量要大于long的容量
4.3 强制类型转换(只涉及7种基本数据类型）：自动类型提升运算的逆运算。
1.需要使用强转符：()
2.注意点：强制类型转换，可能导致精度损失。
4.4 String与8种基本数据类型间的运算
1. String属于引用数据类型,翻译为：字符串
2. 声明String类型变量时，使用一对""
3. String可以和8种基本数据类型变量做运算，且运算只能是连接运算：+
4. 运算的结果仍然是String类型