Java development general methods and guidelines
Do not use confusing letters in variables and constants: int i=1l ;
Don't make constants into variables;
The value type of the ternary operator must be consistent;
Avoid method overloading with variable-length parameters: Java 5 introduced variable-length parameters, varags, represented by ... , the variable-length parameter must be the last parameter, and a method cannot have multiple variable-length parameters;
Don't let null and null values affect variable-length methods, mainly in the overloading of variable-length methods;
Less use of static imports: such as excessive use of import static XXX , the maintainability is reduced
Do not overwrite statically imported variables and methods in this class. Be careful of the compiler's shortest path principle: variables, constants, and methods that can be found in this class will not be found in other packages or parent classes. Properties and methods take precedence.
Avoid assigning final constants in the constructor of serialized classes
Volatile business written in scripting language: can be released at any time without redeployment
basic type
Use even numbers to judge, not odd numbers: use i%2==0 instead of i%2==1 , because i=-1 will be judged as an even number
Use integer type to process currency: first expand N times processing operation, divide N times when displaying
Pay attention to the boundary: such as int n=1000, int input+n<2000, when the input input exceeds the maximum value of Int , the input+n is a negative number and still meets the conditions
Don't let rounding be a loss, avoid it with the RoundingMode class, which provides the Round mode
== in Java is to judge whether the two operands are equal, if it is an object, then judge whether the reference is the same
class, object, method
There should be no implementation code in the interface;
Static variables must be declared before assignment
Do not overwrite static methods
The constructor should be as simple as possible, not throwing exceptions as much as possible, and not doing complex algorithms
Avoid initializing other classes in the constructor
Use the construction code block to refine the program: there is no prefix, just pick it up with {} , the compiler will insert the construction code block directly into the front end of the constructor; but when the this keyword is encountered, the constructor will not be inserted.
Use static inner classes to improve encapsulation
Making Multiple Inheritance a Reality: Implementing with Inner Classes
Make the utility class uninstantiable: in addition to setting the constructor to private , throw an exception
Copying objects using serialization
Overriding equals must implement the HashCOde method
It is recommended to override the tostring method
string
String对象直接赋值，不用new
Java为了避免在一个系统中产生大量String对象，设计了string池。创建机制：创建一个字符串时，先检查池中是否有字面值相等的字符串，有的话则指向该引用；无的话才创建。
Intern方法会检查当前对象在字符串对象池中是否有字面值相等的字符串，有的话则指向该引用；无的话才放在池中。
准确适用String、StringBuffer、StringBuilder
String是不可改变的量，创建后不再修改；
StringBuffer是一个可变字符串，StringBuffer的append与String的“+”的区别的，+之后对应的引用变了，StringBuffer的引用不变值在变。
StringBuilder是线程不安全的， StringBuffer是线程安全的
建议使用UTF8编码
中文字符串排序最好指定Collector排序
Comparator c = Collector.getInstance(Local.CHINA);
Arrays.sort(sre,c)
异常
提倡异常封装：尽量try catch 不抛出
采用异常链传递异常
不要再finally中处理返回值
多线程合并发
不推荐覆写start方法
不用过时的stop方法停止线程
性能和效率
不在循环条件中计算
除非必要，不要克隆对象
调整JVM参数