Less Code == [Less Bugs,Better Readability,Less programmers to hire, Less organizational communication costs, Less maitain cost]
Less Code != [Higher Productivity,Better Performance]
1, import static
remove duplicated namespace
what does it do?
package com.toolbox.lang;
public class ClassWithStaticMember {
public static final String name="value";
public static String say() {
return "111";
}
public static String say(String msg) {
return msg;
}
}
package com.toolbox.lang;
import static com.toolbox.lang.ClassWithStaticMember.say;
import static com.toolbox.lang.ClassWithStaticMember.name;
public class Test {
public static void main(String[] args) {
System.out.println(say());
System.out.println(say(name));
}
}
import同名的member
意味著不同方法簽名的member都會import, e.g. say() and say(String msg)
const #45 = Method #46.#48; // com/toolbox/lang/ClassWithStaticMember.say:()Ljava/lang/String;
const #46 = class #47; // com/toolbox/lang/ClassWithStaticMember
const #47 = Asciz com/toolbox/lang/ClassWithStaticMember;
const #48 = NameAndType #49:#38;// say:()Ljava/lang/String;
const #49 = Asciz say;
const #62 = Method #46.#63; // com/toolbox/lang/ClassWithStaticMember.say:(Ljava/lang/String;)Ljava/lang/String;
const #63 = NameAndType #49:#64;// say:(Ljava/lang/String;)Ljava/lang/String;
copy primitive type value
意味著編譯后，Test class中static import的String, int 等是值的寫入class中，不會在去引用ClassWithStaticMember
43: ldc #55; //String value
45: invokestatic #57; //Method com/toolbox/lang/ClassWithStaticMember.say:(Ljava/lang/String;)Ljava/lang/String;
48: invokevirtual #50; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
when to use it?
Do it when frequent access to static members from one or two classes
Not Do it when has naming conflict or complicated class body, otherwise, make you confuse with so many polluting namespace
2, apply lanuage feature
2.1 String contact
String s = "a" + "b";
compile into:
const #15 = Asciz ([Ljava/lang/String;)V;
const #16 = String #17; // ab
if String constance + String constance
直接編譯成結果寫入class
else
使用StringBuilder.append
So always use "+" unless you need to use StringBuffer or other specific class
3, inner class {{}}
List<String> list = new ArrayList<String>() {{add("data1");add("data2");}};
4, use PMD to find and remove duplicated code
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文章來源:
http://sevenduan.javaeye.com/blog/504911