刚开始学习java的时候，finally，return是个头疼的问题，面试题里天天都是问谁先执行？
下面我们就结合《深入java虚拟机》第18章 finally子语句和例子对应的字节码来探讨一下这个问题
看此篇文章之前可以看看前面一篇文章描述finally字节码：
http://abc08010051.iteye.com/admin/blogs/2154981
例子1：
public static int tt1() {
int b = 23;
try {
System.out.println("yes");
return b += 88;
} catch (Exception e) {
System.out.println("error : " + e);
} finally {
if (b > 25) {
System.out.println("b>25 : " + b);
}
System.out.println("finally");
}
return b;
}
代码执行结果：
yes b>25 : 111 finally 111
bytecode:
bipush 23 //把23压入栈 istore_0 //把23放到位置为0的局部变量中 getstatic java/lang/System/out Ljava/io/PrintStream; ldc "yes" //把常量“yes”压入栈 invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V //打印"yes" iinc 0 88 //位置为0的变量值加88 iload_0 //把位置为0的局部变量（值为111）压入栈 istore_1 //把栈顶元素出栈，（栈顶元素为111），并赋值给位置为1的局部变量 iload_0 //把位置为0的局部变量值压入栈 bipush 25 //把25压入栈 if_icmple 22 //比较栈顶两个int类型的值，如果小于0调到22执行 getstatic java/lang/System/out Ljava/io/PrintStream; //此行到22行，通过StringBuilder构建字符串"b>25 : "加上b（即位置为0的局部变量值），并打印字符串 new java/lang/StringBuilder dup invokespecial java/lang/StringBuilder/<init>()V ldc "b>25 : " invokevirtual java/lang/StringBuilder/append(Ljava/lang/String;)Ljava/lang/StringBuilder; iload_0 invokevirtual java/lang/StringBuilder/append(I)Ljava/lang/StringBuilder; invokevirtual java/lang/StringBuilder/toString()Ljava/lang/String; invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V //从11行到此行，通过StringBuilder构建字符串"b>25 : "加上b（即位置为0的局部变量值），并打印字符串 getstatic java/lang/System/out Ljava/io/PrintStream; ldc "finally" invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V //打印“finally”字符串 iload_1 //获取位置为1的局部变量的值并压入栈中 ireturn //返回栈顶的int值 astore_1 getstatic java/lang/System/out Ljava/io/PrintStream; new java/lang/StringBuilder dup invokespecial java/lang/StringBuilder/<init>()V ldc "error : " invokevirtual java/lang/StringBuilder/append(Ljava/lang/String;)Ljava/lang/StringBuilder; aload_1 invokevirtual java/lang/StringBuilder/append(Ljava/lang/Object;)Ljava/lang/StringBuilder; invokevirtual java/lang/StringBuilder/toString()Ljava/lang/String; invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V iload_0 bipush 25 if_icmple 51 getstatic java/lang/System/out Ljava/io/PrintStream; new java/lang/StringBuilder dup invokespecial java/lang/StringBuilder/<init>()V ldc "b>25 : " invokevirtual java/lang/StringBuilder/append(Ljava/lang/String;)Ljava/lang/StringBuilder; iload_0 invokevirtual java/lang/StringBuilder/append(I)Ljava/lang/StringBuilder; invokevirtual java/lang/StringBuilder/toString()Ljava/lang/String; invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V getstatic java/lang/System/out Ljava/io/PrintStream; ldc "finally" invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V goto 74 astore_2 iload_0 bipush 25 if_icmple 69 getstatic java/lang/System/out Ljava/io/PrintStream; new java/lang/StringBuilder dup invokespecial java/lang/StringBuilder/<init>()V ldc "b>25 : " invokevirtual java/lang/StringBuilder/append(Ljava/lang/String;)Ljava/lang/StringBuilder; iload_0 invokevirtual java/lang/StringBuilder/append(I)Ljava/lang/StringBuilder; invokevirtual java/lang/StringBuilder/toString()Ljava/lang/String; invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V getstatic java/lang/System/out Ljava/io/PrintStream; ldc "finally" invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V aload_2 athrow iload_0 ireturn//对应代码最后的return
上面的字节码值解释了我们方法正常执行的部分，由上面的字节码解释我们知道：return语句时在finally例程执行之后才执行的
例子2：
这个例子和上面的那个差不多，差别是在finally语句块里对变量进行了操作：
public static int tt2() {
int b = 23;
try {
System.out.println("yes");
return b += 88;
} catch (Exception e) {
System.out.println("error : " + e);
} finally {
if(b>25)
{
System.out.println("b>25 : "+b);
}
System.out.println("finally");
b = 100;
}
return b;
} 执行结果：
yes b>25 : 111 finally 111这个结果很令人诧异，如果按照例子1得出来的结论，return 在finally语句块之后执行，那么输出结果应该是：
yes b>25 : 111 finally 100
这是为什么呢？
我们来看看tt2()方法的字节码：
bipush 23 //把23压入栈 istore_0 //把23放到位置为0的局部变量中 getstatic java/lang/System/out Ljava/io/PrintStream; ldc "yes" //把常量“yes”压入栈 invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V //打印"yes" iinc 0 88 //位置为0的变量值加88 iload_0 //把位置为0的局部变量（值为111）压入栈 istore_1 //把栈顶元素出栈，（栈顶元素为111），并赋值给位置为1的局部变量 iload_0 //把位置为0的局部变量值压入栈 bipush 25 //把25压入栈 if_icmple 22 //比较栈顶两个int类型的值，如果小于0调到22执行 getstatic java/lang/System/out Ljava/io/PrintStream; //此行到22行，通过StringBuilder构建字符串"b>25 : "加上b（即位置为0的局部变量值），并打印字符串 new java/lang/StringBuilder dup invokespecial java/lang/StringBuilder/<init>()V ldc "b>25 : " invokevirtual java/lang/StringBuilder/append(Ljava/lang/String;)Ljava/lang/StringBuilder; iload_0 invokevirtual java/lang/StringBuilder/append(I)Ljava/lang/StringBuilder; invokevirtual java/lang/StringBuilder/toString()Ljava/lang/String; invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V //从11行到此行，通过StringBuilder构建字符串"b>25 : "加上b（即位置为0的局部变量值），并打印字符串 getstatic java/lang/System/out Ljava/io/PrintStream; ldc "finally" invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V //打印“finally”字符串 bipush 100 //把100压入栈顶 istore_0 //把栈顶值（100）弹出栈，并赋值给位置为0的局部变量（代码中的b） iload_1 //把位置为1的局部变量（111）压入栈 ireturn //弹出栈顶的int值，返回，退出方法 astore_1 getstatic java/lang/System/out Ljava/io/PrintStream; new java/lang/StringBuilder dup invokespecial java/lang/StringBuilder/<init>()V ldc "error : " invokevirtual java/lang/StringBuilder/append(Ljava/lang/String;)Ljava/lang/StringBuilder; aload_1 invokevirtual java/lang/StringBuilder/append(Ljava/lang/Object;)Ljava/lang/StringBuilder; invokevirtual java/lang/StringBuilder/toString()Ljava/lang/String; invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V iload_0 bipush 25 if_icmple 53 getstatic java/lang/System/out Ljava/io/PrintStream; new java/lang/StringBuilder dup invokespecial java/lang/StringBuilder/<init>()V ldc "b>25 : " invokevirtual java/lang/StringBuilder/append(Ljava/lang/String;)Ljava/lang/StringBuilder; iload_0 invokevirtual java/lang/StringBuilder/append(I)Ljava/lang/StringBuilder; invokevirtual java/lang/StringBuilder/toString()Ljava/lang/String; invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V getstatic java/lang/System/out Ljava/io/PrintStream; ldc "finally" invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V bipush 100 istore_0 goto 80 astore_2 iload_0 bipush 25 if_icmple 73 getstatic java/lang/System/out Ljava/io/PrintStream; new java/lang/StringBuilder dup invokespecial java/lang/StringBuilder/<init>()V ldc "b>25 : " invokevirtual java/lang/StringBuilder/append(Ljava/lang/String;)Ljava/lang/StringBuilder; iload_0 invokevirtual java/lang/StringBuilder/append(I)Ljava/lang/StringBuilder; invokevirtual java/lang/StringBuilder/toString()Ljava/lang/String; invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V getstatic java/lang/System/out Ljava/io/PrintStream; ldc "finally" invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V bipush 100 istore_0 aload_2 athrow iload_0 ireturn
从上面的字节码可以看出，return还是在finally语句块之后执行， 返回111而不是100的原因可以参考上面标注为红色的bytecode解释，
当代码执行到“return b += 88;” 这一行时，jvm把局部变量b加88，加后的局部变量b存放在位置为0的变量中，然后把b的值复制存放到位置为1的局部变量中，
执行finally语句块时，对局部变量b进行操作，在虚拟机内部只是对位置为0的变量进行操作，当返回时，虚拟机返回的是位置为1的变量值，即为111
深入java虚拟机也有此解释：
例子3：
public static int tt3() {
int b = 23;
try {
System.out.println("yes");
return b += 88;
} catch (Exception e) {
System.out.println("error : " + e);
} finally {
if(b>25)
{
System.out.println("b>25 : "+b);
}
System.out.println("finally");
b = 100;
return b;
}
} 执行结果：
yes b>25 : 111 finally 100根据结果判断，在执行“return b += 88;”这行代码的时候，把表达式“b += 88;”执行以后去执行finally语句块执行，在finally语句中return，退出方法
