|Syntax error on token "const", delete this token|
Consider the following declaration at the top of a class:static int intVal = 42; static String strVal = "Hello, world!";
The compiler generates a class initializer method, called
<clinit>, that is executed when the class is first used. The method stores the value 42 into
intVal, and extracts a reference from the classfile string constant table for
strVal. When these values are referenced later on, they are accessed with field lookups.
We can improve matters with the "final" keyword:static final int intVal = 42; static final String strVal = "Hello, world!";
The class no longer requires a
<clinit>method, because the constants go into classfile static field initializers, which are handled directly by the VM. Code accessing
intValwill use the integer value 42 directly, and accesses to
strValwill use a relatively inexpensive "string constant" instruction instead of a field lookup.
Declaring a method or class "final" does not confer any immediate performance benefits, but it does allow certain optimizations. For example, if the compiler knows that a "getter" method can’t be overridden by a sub-class, it can inline the method call.
You can also declare local variables final. However, this has no definitive performance benefits. For local variables, only use "final" if it makes the code clearer (or you have to, e.g. for use in an anonymous inner class).
static final String stHtmlCharset = "GB18030";
把const xxx 改为：static final xxx，就可以实现了基本的const的效果了。