常量入栈指令有iconst、bipush、sipush、ldc、ldc2_w分别对应不同的使用场景
以下两个表简单总结了使用场景
八大基本类型场景表
常量类型 | 常量范围 | 指令 |
整型int | -1~5 | iconst_0~ iconst_5 iconst_m1 |
-128~127 | bipush | |
-32768~32767 | sipush | |
-2147483648~2147483647 | #2 = Integer 12345678 0: ldc #2 // int 12345678 | |
布尔型boolean | true | iconst_1 |
false | iconst_0 | |
短整型short | -1~5 | iconst_0~ iconst_5 iconst_m1 |
-128~127 | bipush | |
-32768~32767 | sipush | |
字符型char | \u0000~\u0005 | iconst_0~ iconst_5 |
\u0000~\u00FF | bipush | |
\u0000~\uFFFF | sipush | |
字节型byte | -1~5 | iconst_0~ iconst_5 iconst_m1 |
-128~127 | bipush | |
长整型long | -2^63~2^63-1 | #2 = Long 1234567890123456789l ldc2_w #2 // long 1234567890123456789l |
浮点型double | 8字节 | #2 = Double 123.456d ldc2_w #2 // double 123.456d |
浮点型float | 4字节 | #2 = Float 123.456f ldc #2 // float 123.456f |
指令场景表
指令 | 使用场景 |
iconst | int,short,byte,int(char a)数值在-1~5之间，boolean类型，注意不包括long |
bipush | int,short,byte,int(char a)数值在-128~127之间，注意不包括long，范围内的值在iconst之内的优先用iconst |
sipush | int,short,int(char a)数值在-32768~32767之间，boolean类型，注意不包括long，范围内的值在bipush之内的优先用bipush |
ldc | int的数值-2147483648~2147483647之间（范围内的值在sipush之内的优先用sipush），float类型 |
ldc2_w | long类型，double类型 |
以下是简单的例子
整型常量0的例子iconst
public class ret{public static int main(String[] args){return 0;}}编译
javac ret.java
Java标准反编译
javap -c -verbose ret.class
...major version: 52...public static int main(java.lang.String[]);descriptor: ([Ljava/lang/String;)Iflags: ACC_PUBLIC, ACC_STATICCode:stack=1, locals=1, args_size=10: iconst_01: ireturnLineNumberTable:line 5: 0
注意其中的0: iconst_0即可
整型常量123的例子bipush
public class ret{public static int main(String[] args){return 123;}}反编译
...major version: 52...public static int main(java.lang.String[]);descriptor: ([Ljava/lang/String;)Iflags: ACC_PUBLIC, ACC_STATICCode:stack=1, locals=1, args_size=10: bipush 1232: ireturnLineNumberTable:line 5: 0
注意其中的0: bipush 123
整型常量1234的例子sipush
public class ret{public static int main(String[] args){return 1234;}}反编译
...major version: 52...public static int main(java.lang.String[]);descriptor: ([Ljava/lang/String;)Iflags: ACC_PUBLIC, ACC_STATICCode:stack=1, locals=1, args_size=10: sipush 12343: ireturnLineNumberTable:line 5: 0
注意其中的 0: sipush 1234
整型常量12345678的例子ldc
public class ret{public static int main(String[] args){return 12345678;}}反编译
...major version: 52...#2 = Integer 12345678...public static int main(java.lang.String[]);descriptor: ([Ljava/lang/String;)Iflags: ACC_PUBLIC, ACC_STATICCode:stack=1, locals=1, args_size=10: ldc #2 // int 123456782: ireturnLineNumberTable:line 5: 0
布尔型true例子iconst
public class ret{public static boolean main(String[] args){return true;}}反编译
...major version: 52...public static boolean main(java.lang.String[]);descriptor: ([Ljava/lang/String;)Zflags: ACC_PUBLIC, ACC_STATICCode:stack=1, locals=1, args_size=10: iconst_11: ireturnLineNumberTable:line 5: 0
注意0: iconst_1即ture用常量1表示
短整型short例子
public class ret{public static short main(String[] args){return 1234;}}反编译
...major version: 52...public static short main(java.lang.String[]);descriptor: ([Ljava/lang/String;)Sflags: ACC_PUBLIC, ACC_STATICCode:stack=1, locals=1, args_size=10: sipush 12343: ireturnLineNumberTable:line 5: 0
注意0: sipush 1234
字符型A例子
public class ret{public static char main(String[] args){return 'A';}}反编译
...major version: 52...public static char main(java.lang.String[]);descriptor: ([Ljava/lang/String;)Cflags: ACC_PUBLIC, ACC_STATICCode:stack=1, locals=1, args_size=10: bipush 652: ireturnLineNumberTable:line 5: 0
注意0: bipush 65
字符型中例子
public class ret{public static char main(String[] args){return '中';}}反编译
...major version: 52...public static char main(java.lang.String[]);descriptor: ([Ljava/lang/String;)Cflags: ACC_PUBLIC, ACC_STATICCode:stack=1, locals=1, args_size=10: sipush 200133: ireturnLineNumberTable:line 5: 0
注意0: sipush 20013
byte类型123列子
public class ret{public static byte main(String[] args){return 123;}}反编译
...major version: 52...public static byte main(java.lang.String[]);descriptor: ([Ljava/lang/String;)Bflags: ACC_PUBLIC, ACC_STATICCode:stack=1, locals=1, args_size=10: bipush 1232: ireturnLineNumberTable:line 5: 0
注意 0: bipush 123
long类型1234567890123456789L例子
public class ret{public static long main(String[] args){return 1234567890123456789l;}}反编译
...major version: 52...#2 = Long 1234567890123456789l...public static long main(java.lang.String[]);descriptor: ([Ljava/lang/String;)Jflags: ACC_PUBLIC, ACC_STATICCode:stack=2, locals=1, args_size=10: ldc2_w #2 // long 1234567890123456789l3: lreturnLineNumberTable:line 5: 0
注意0: ldc2_w #2 // long 1234567890123456789l
浮点类型123.456d的例子
public class ret{public static double main(String[] args){return 123.456d;}}反编译
...major version: 52...#2 = Double 123.456d...public static double main(java.lang.String[]);descriptor: ([Ljava/lang/String;)Dflags: ACC_PUBLIC, ACC_STATICCode:stack=2, locals=1, args_size=10: ldc2_w #2 // double 123.456d3: dreturnLineNumberTable:line 5: 0
注意0: ldc2_w #2 // double 123.456d
浮点类型123.456f的例子
public class ret{public static float main(String[] args){return 123.456f;}}反编译
...major version: 52...#2 = Float 123.456f...public static float main(java.lang.String[]);descriptor: ([Ljava/lang/String;)Fflags: ACC_PUBLIC, ACC_STATICCode:stack=1, locals=1, args_size=10: ldc #2 // float 123.456f2: freturnLineNumberTable:line 5: 0
注意0: ldc #2 // float 123.456f
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