How switch cases are executed for strings?

问题

I have a doubt in switch-case statement. Here is my code :

String month = "April";
switch (month.toLowerCase()) {
            case "january":
                monthNumber = 1;
                break;
            case "february":
                monthNumber = 2;
                break;
            case "march":
                monthNumber = 3;
                break;
            case "april":
                monthNumber = 4;
                break;

and so on..

I have 3 questions in this context:

1) While comparing month with the case values i.e case "January", case "February" .. What is exactly used from the following by compiler ?? - month.equals("case-value") ? - month == case-value ?

2) And are case-values internally converted to StringBuilder/StringStringBuffer or simply they remain String object ??

3) How I can I know this from byte code i.e is there any tool available using which I can view directly the compiler generated code just to find out how the things behave internally?

回答1:

3) I believe JDeveloper has bytecode debugger feature. If JDeveloper is not and option, check out these tools I found:

http://sourceforge.net/projects/jbcd/

http://andrei.gmxhome.de/bytecode/index.html

http://www.drgarbage.com/how-to-debug-bytecode-with-bytecode-visualizer.html

回答2:

Not sure about number 3 but looking at the byte code is probably too low level to easily see what methods are being used.

1) the strings are compared using .equals().

2) the strings remain as String objects

See: http://docs.oracle.com/javase/tutorial/java/nutsandbolts/switch.html

回答3:

1 - The String in the switch expression is compared with the expressions associated with each case label as if the String.equals method were being used.

2 - Normal String object is used for this switch case statement

http://blogs.oracle.com/darcy/entry/project_coin_string_switch_anatomy

来源：https://stackoverflow.com/questions/9124658/how-switch-cases-are-executed-for-strings

标签

java

compiler-construction

switch-statement

bytecode