Java 语法糖 - 增强 for 循环
Java About 4,190 words本质
对于数组而言,会转换为普通for
循环。
对于集合而言,会转换为iterator
迭代器。
数组
对于数组而言,增强for
循环本质是for(int i = 0; i < arr.length(); ++i)
。
Java 代码
public class Test4 {
public static void main(String[] args) {
int[] arr = {1, 2, 3};
for (int i : arr) {
}
}
}
反编译 class
可以看到:
编译成字节码后,转换成了普通for
循环。(可以使用反编译工具,或者直接在IDEA
中打开.class
文件)
public class Test4 {
public Test4() {
}
public static void main(String[] args) {
int[] arr = new int[]{1, 2, 3};
int[] var2 = arr;
int var3 = arr.length;
for(int var4 = 0; var4 < var3; ++var4) {
int var10000 = var2[var4];
}
}
}
字节码
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: (0x0009) ACC_PUBLIC, ACC_STATIC
Code:
stack=4, locals=6, args_size=1
0: iconst_3
1: newarray int
3: dup
4: iconst_0
5: iconst_1
6: iastore
7: dup
8: iconst_1
9: iconst_2
10: iastore
11: dup
12: iconst_2
13: iconst_3
14: iastore
15: astore_1
16: aload_1
17: astore_2
18: aload_2
19: arraylength
20: istore_3
21: iconst_0
22: istore 4
24: iload 4
26: iload_3
27: if_icmpge 42
30: aload_2
31: iload 4
33: iaload
34: istore 5
36: iinc 4, 1
39: goto 24
42: return
LineNumberTable:
line 6: 0
line 7: 16
line 10: 42
LocalVariableTable:
Start Length Slot Name Signature
0 43 0 args [Ljava/lang/String;
16 27 1 arr [I
StackMapTable: number_of_entries = 2
frame_type = 255 /* full_frame */
offset_delta = 24
locals = [ class "[Ljava/lang/String;", class "[I", class "[I", int, int ]
stack = []
frame_type = 248 /* chop */
offset_delta = 17
MethodParameters:
Name Flags
args
集合
Java 代码
public class Test5 {
public static void main(String[] args) {
ArrayList<Integer> list = new ArrayList<>();
for (Integer integer : list) {
}
}
}
反编译 class
可以看到:
编译成字节码后,转换成了iterator
迭代器。
public class Test5 {
public Test5() {
}
public static void main(String[] args) {
ArrayList<Integer> list = new ArrayList();
Integer var3;
for(Iterator var2 = list.iterator(); var2.hasNext(); var3 = (Integer)var2.next()) {
}
}
}
字节码
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: (0x0009) ACC_PUBLIC, ACC_STATIC
Code:
stack=2, locals=4, args_size=1
0: new #2 // class java/util/ArrayList
3: dup
4: invokespecial #3 // Method java/util/ArrayList."<init>":()V
7: astore_1
8: aload_1
9: invokevirtual #4 // Method java/util/ArrayList.iterator:()Ljava/util/Iterator;
12: astore_2
13: aload_2
14: invokeinterface #5, 1 // InterfaceMethod java/util/Iterator.hasNext:()Z
19: ifeq 35
22: aload_2
23: invokeinterface #6, 1 // InterfaceMethod java/util/Iterator.next:()Ljava/lang/Object;
28: checkcast #7 // class java/lang/Integer
31: astore_3
32: goto 13
35: return
LineNumberTable:
line 8: 0
line 9: 8
line 11: 32
line 12: 35
LocalVariableTable:
Start Length Slot Name Signature
0 36 0 args [Ljava/lang/String;
8 28 1 list Ljava/util/ArrayList;
LocalVariableTypeTable:
Start Length Slot Name Signature
8 28 1 list Ljava/util/ArrayList<Ljava/lang/Integer;>;
StackMapTable: number_of_entries = 2
frame_type = 253 /* append */
offset_delta = 13
locals = [ class java/util/ArrayList, class java/util/Iterator ]
frame_type = 250 /* chop */
offset_delta = 21
MethodParameters:
Name Flags
args
Views: 1,706 · Posted: 2022-04-27
————        END        ————
Give me a Star, Thanks:)
https://github.com/fendoudebb/LiteNote扫描下方二维码关注公众号和小程序↓↓↓
Loading...