java boolean占用内存是多少

一，结论

关于boolean占用内存是多少，我在JVM规范中找到以下解释，但是怎么验证呢？

虚拟机没有给boolean(布尔)类型设置单独指令。boolean型的数据是有integer指令，包括interger返回来处理的。boolean型数组则是用byte数组来处理的。

二，验证

写了两个简单的程序，使用jclasslib查看字节码，对照Java虚拟机指令集后验证结论正确。

 Chapter 6. The Java Virtual Machine Instruction Set

1，boolean型的数据=>32位

代码

public class Test1Type {
 
    public static void main(String[] args) {
 
        boolean a=true;
        byte b=1;
        System.out.println(a);
        System.out.println(b);
    }
}

对照图

2，boolean数组型=>8位

代码

public class Test1Type {
 
    public static void main(String[] args) {
 
        boolean[] a=new boolean[]{true};
        byte[] b=new byte[]{1};
        System.out.println(a[0]);
        System.out.println(b[0]);
    }
}

对照图

三，查看字节码

如果没有安装jclasslib可以使用javap

javap -v Test1Type.class

输出结果：

D:\Program Files\JetBrains\idea18\work\nacos-develop\demo\core\target\test-classes>javap -v Test1Type.class
Classfile /D:/Program Files/JetBrains/idea18/work/nacos-develop/demo/core/target/test-classes/Test1Type.class
  Last modified 2023-9-18; size 589 bytes
  MD5 checksum dafc695ce0954b2a996cc96f815ba6f3
  Compiled from "Test1Type.java"
public class Test1Type
  minor version: 0
  major version: 52
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Methodref          #6.#24         // java/lang/Object."":()V
   #2 = Fieldref           #25.#26        // java/lang/System.out:Ljava/io/PrintStream;
   #3 = Methodref          #27.#28        // java/io/PrintStream.println:(Z)V
   #4 = Methodref          #27.#29        // java/io/PrintStream.println:(I)V
   #5 = Class              #30            // Test1Type
   #6 = Class              #31            // java/lang/Object
   #7 = Utf8               
   #8 = Utf8               ()V
   #9 = Utf8               Code
  #10 = Utf8               LineNumberTable
  #11 = Utf8               LocalVariableTable
  #12 = Utf8               this
  #13 = Utf8               LTest1Type;
  #14 = Utf8               main
  #15 = Utf8               ([Ljava/lang/String;)V
  #16 = Utf8               args
  #17 = Utf8               [Ljava/lang/String;
  #18 = Utf8               a
  #19 = Utf8               [Z
  #20 = Utf8               b
  #21 = Utf8               [B
  #22 = Utf8               SourceFile
  #23 = Utf8               Test1Type.java
  #24 = NameAndType        #7:#8          // "":()V
  #25 = Class              #32            // java/lang/System
  #26 = NameAndType        #33:#34        // out:Ljava/io/PrintStream;
  #27 = Class              #35            // java/io/PrintStream
  #28 = NameAndType        #36:#37        // println:(Z)V
  #29 = NameAndType        #36:#38        // println:(I)V
  #30 = Utf8               Test1Type
  #31 = Utf8               java/lang/Object
  #32 = Utf8               java/lang/System
  #33 = Utf8               out
  #34 = Utf8               Ljava/io/PrintStream;
  #35 = Utf8               java/io/PrintStream
  #36 = Utf8               println
  #37 = Utf8               (Z)V
  #38 = Utf8               (I)V
{
  public Test1Type();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial #1                  // Method java/lang/Object."":()V
         4: return
      LineNumberTable:
        line 1: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0       5     0  this   LTest1Type;
 
  public static void main(java.lang.String[]);
    descriptor: ([Ljava/lang/String;)V
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=4, locals=3, args_size=1
         0: iconst_1
         1: newarray       boolean
         3: dup
         4: iconst_0
         5: iconst_1
         6: bastore
         7: astore_1
         8: iconst_1
         9: newarray       byte
        11: dup
        12: iconst_0
        13: iconst_1
        14: bastore
        15: astore_2
        16: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
        19: aload_1
        20: iconst_0
        21: baload
        22: invokevirtual #3                  // Method java/io/PrintStream.println:(Z)V
        25: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
        28: aload_2
        29: iconst_0
        30: baload
        31: invokevirtual #4                  // Method java/io/PrintStream.println:(I)V
        34: return
      LineNumberTable:
        line 5: 0
        line 6: 8
        line 8: 16
        line 9: 25
        line 10: 34
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      35     0  args   [Ljava/lang/String;
            8      27     1     a   [Z
           16      19     2     b   [B
}
SourceFile: "Test1Type.java"