1、Java运算符优先级：
Operator Precedence
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Operators
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Associativity
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[] . () (method call)
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Left to right
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! ~ ++ -- + (unary) – (unary) ()
(cast) new
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Right to left
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* / %
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Left to right
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+ -
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Left to right
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<< >> >>>
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Left to right
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< <= > >= instanceof
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Left to right
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== !=
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Left to right
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&
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Left to right
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^
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Left to right
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Left to right
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&&
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Left to right
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||
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Left to right
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?:
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Right to left
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= += -= *= /= %= &= |= ^= <<= >>=
>>>=
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Right to left
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注意：
- && || ! 的操作数只能用于boolean 或 Boolean
- & | 的操作数既可以用于boolean(Boolean)或者整形(不仅仅是int型），但两个操作数的类型必须一致
- ~不能用于boolean(Boolean)型，但可以用于整形，大概是为了和 ! 区别开来吧
- & | 没有短路计算的
2、
Java Integer Types
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Type
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Storage Requirement
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Range
(Inclusive)
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int
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4 bytes
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–2,147,483,648 to 2,147,483,647 (just over 2 billion)
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short
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2 bytes
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–32,768 to 32,767
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long
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8 bytes
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–9,223,372,036,854,775,808 to
9,223,372,036,854,775,807
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byte
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1 byte
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–128 to 127
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char 2 bytes 0 to 65535
3、
Floating-Point Types
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Type
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Storage Requirement
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Range
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float
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4 bytes
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approximately ±3.40282347E+38F (6–7 significant decimal
digits)
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double
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8 bytes
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approximately ±1.79769313486231570E+308 (15 significant decimal
digits)
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4、final 实例域（final instance field)：可以将实例域定义为final，构建对象时必须初始化这样得域，也就是说，必须确保在每一个构造器执行之后，这个域的值被设置。但是，静态常量必须在声明的同时也被初始化。
5、for each 循环：
for (variable : collection) statment
例如：for (int element : a)
System.out.println(element);
该代码片段打印数组a的每一个元素，一个元素占一行
6、合法的Java标识符：可以以下划线、字母或美元符号$开头，后面可以跟下划线、数字、字母、美元符号。1.42以后的java标识符也可以包含汉字，包括开头。