invokevirtual，invokespecial，invokestatic，invokein

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本文通过实验对比了Java中invokevirtual、invokespecial、invokestatic及invokeinterface四种方法调用指令的性能差异。结果显示静态方法调用速度最快，而接口方法调用则相对较慢。

invokevirtual，invokespecial，invokestatic，invokeinterface

invokevirtual 调用类实例方法，方法引用
        栈：
        前：。。。，objectref，[arg1,[arg2......]]
        后：。。。
invlkestatic 调用类方法，不需要建新建类实例,此时操作数栈只要保存留参数即可
        栈：
        前：。。。，[arg1,[arg2.....]]
        后：。。。
invokespecial 使用对私有方法，超类方法和实例初始化方法的特殊处理来调用实例方法。
        栈：
        前：。。。，objectref，[arg1,[arg2......]]
        后：。。。
invokeinterface 调用接口方法
        栈：
        前：。。。，objectref，[arg1,[arg2......]]
        后：。。。

程序如下：

package yhs.test;

public interface Iface {
    public void test();
}

package yhs.test;

public class Impl
  implements Iface {

    public void test() {
    }

    public static void testStatic() {
    }

    private void testPrivate() {
    }

    //--------------------------------------------------------------------------
    //--------------------------------------------------------------------------
    public static void main(String[] args) {
        Impl impl = new Impl();
        Iface iface = impl;

        //热身
        int count = 10000000;
        for (int i = 0; i < count; i++) {
            impl.test();
            impl.testPrivate();
            Impl.testStatic();
            iface.test();
        }

        //开始测试
        count = 100000000;

        long t1 = System.currentTimeMillis();
        for (int i = 0; i < count; i++) {
            impl.test();
        }
        System.out.println("invokevirtual:   " +
                           (System.currentTimeMillis() - t1));

        t1 = System.currentTimeMillis();
        for (int i = 0; i < count; i++) {
            impl.testPrivate();
        }
        System.out.println("invokespecial:   " +
                           (System.currentTimeMillis() - t1));

        t1 = System.currentTimeMillis();
        for (int i = 0; i < count; i++) {
            Impl.testStatic();
        }
        System.out.println("invokestatic:    " +
                           (System.currentTimeMillis() - t1));

        t1 = System.currentTimeMillis();
        for (int i = 0; i < count; i++) {
            iface.test();
        }
        System.out.println("invokeinterface: " +
                           (System.currentTimeMillis() - t1));
    }
}

反汇编Impl.class产生的字节码如下：

public class yhs.test.Impl extends java.lang.Object implements yhs.test.Iface{
public yhs.test.Impl();
Code:
   0:   aload_0
   1:   invokespecial   #1; //Method java/lang/Object."":()V
   4:   return

public void test();
Code:
   0:   return

public static void testStatic();
Code:
   0:   return

public static void main(java.lang.String[]);
Code:
   0:   new     #2; //class Impl
   3:   dup
   4:   invokespecial   #3; //Method "":()V
   7:   astore_1
   8:   aload_1
   9:   astore_2
   //---------------------------------------------------------------------------------------------
   10: ldc     #4; //int 10000000
   12: istore_3
   13: iconst_0
   14: istore 4
   16: goto    39
   19: aload_1
   20: invokevirtual   #5; //Method test:()V
   23: aload_1
   24: invokespecial   #6; //Method testPrivate:()V
   27: invokestatic    #7; //Method testStatic:()V
   30: aload_2
   31: invokeinterface #8, 1; //InterfaceMethod yhs/test/Iface.test:()V
   36: iinc    4, 1
   39: iload   4
   41: iload_3
   42: if_icmplt       19
   //---------------------------------------------------------------------------------------------
   45: ldc     #9; //int 100000000
   47: istore_3
   48: invokestatic    #10; //Method java/lang/System.currentTimeMillis:()J
   51: lstore 5
   53: iconst_0
   54: istore 7
   56: goto    66
   59: aload_1
   60: invokevirtual   #5; //Method test:()V
   63: iinc    7, 1
   66: iload   7
   68: iload_3
   69: if_icmplt       59
   72: getstatic       #11; //Field java/lang/System.out:Ljava/io/PrintStream;
   75: new     #12; //class StringBuffer
   78: dup
   79: invokespecial   #13; //Method java/lang/StringBuffer."":()V
   82: ldc     #14; //String invokevirtual:
   84: invokevirtual   #15; //Method java/lang/StringBuffer.append:(Ljava/lang/
String;)Ljava/lang/StringBuffer;
   87: invokestatic    #10; //Method java/lang/System.currentTimeMillis:()J
   90: lload   5
   92: lsub
   93: invokevirtual   #16; //Method java/lang/StringBuffer.append:(J)Ljava/lan
g/StringBuffer;
   96: invokevirtual   #17; //Method java/lang/StringBuffer.toString:()Ljava/la
ng/String;
   99: invokevirtual   #18; //Method java/io/PrintStream.println:(Ljava/lang/St
ring;)V
   //---------------------------------------------------------------------------------------------
   102: invokestatic    #10; //Method java/lang/System.currentTimeMillis:()J
   105: lstore 5
   107: iconst_0
   108: istore 8
   110: goto    120
   113: aload_1
   114: invokespecial   #6; //Method testPrivate:()V
   117: iinc    8, 1
   120: iload   8
   122: iload_3
   123: if_icmplt       113
   126: getstatic       #11; //Field java/lang/System.out:Ljava/io/PrintStream;
   129: new     #12; //class StringBuffer
   132: dup
   133: invokespecial   #13; //Method java/lang/StringBuffer."":()V
   136: ldc     #19; //String invokespecial:
   138: invokevirtual   #15; //Method java/lang/StringBuffer.append:(Ljava/lang/
String;)Ljava/lang/StringBuffer;
   141: invokestatic    #10; //Method java/lang/System.currentTimeMillis:()J
   144: lload   5
   146: lsub
   147: invokevirtual   #16; //Method java/lang/StringBuffer.append:(J)Ljava/lan
g/StringBuffer;
   150: invokevirtual   #17; //Method java/lang/StringBuffer.toString:()Ljava/la
ng/String;
   153: invokevirtual   #18; //Method java/io/PrintStream.println:(Ljava/lang/St
ring;)V
   //---------------------------------------------------------------------------------------------
   156: invokestatic    #10; //Method java/lang/System.currentTimeMillis:()J
   159: lstore 5
   161: iconst_0
   162: istore 9
   164: goto    173
   167: invokestatic    #7; //Method testStatic:()V
   170: iinc    9, 1
   173: iload   9
   175: iload_3
   176: if_icmplt       167
   179: getstatic       #11; //Field java/lang/System.out:Ljava/io/PrintStream;
   182: new     #12; //class StringBuffer
   185: dup
   186: invokespecial   #13; //Method java/lang/StringBuffer."":()V
   189: ldc     #20; //String invokestatic:
   191: invokevirtual   #15; //Method java/lang/StringBuffer.append:(Ljava/lang/
String;)Ljava/lang/StringBuffer;
   194: invokestatic    #10; //Method java/lang/System.currentTimeMillis:()J
   197: lload   5
   199: lsub
   200: invokevirtual   #16; //Method java/lang/StringBuffer.append:(J)Ljava/lan
g/StringBuffer;
   203: invokevirtual   #17; //Method java/lang/StringBuffer.toString:()Ljava/la
ng/String;
   206: invokevirtual   #18; //Method java/io/PrintStream.println:(Ljava/lang/St
ring;)V
   //---------------------------------------------------------------------------------------------
   209: invokestatic    #10; //Method java/lang/System.currentTimeMillis:()J
   212: lstore 5
   214: iconst_0
   215: istore 10
   217: goto    229
   220: aload_2
   221: invokeinterface #8, 1; //InterfaceMethod yhs/test/Iface.test:()V
   226: iinc    10, 1
   229: iload   10
   231: iload_3
   232: if_icmplt       220
   235: getstatic       #11; //Field java/lang/System.out:Ljava/io/PrintStream;
   238: new     #12; //class StringBuffer
   241: dup
   242: invokespecial   #13; //Method java/lang/StringBuffer."":()V
   245: ldc     #21; //String invokeinterface:
   247: invokevirtual   #15; //Method java/lang/StringBuffer.append:(Ljava/lang/
String;)Ljava/lang/StringBuffer;
   250: invokestatic    #10; //Method java/lang/System.currentTimeMillis:()J
   253: lload   5
   255: lsub
   256: invokevirtual   #16; //Method java/lang/StringBuffer.append:(J)Ljava/lan
g/StringBuffer;
   259: invokevirtual   #17; //Method java/lang/StringBuffer.toString:()Ljava/la
ng/String;
   262: invokevirtual   #18; //Method java/io/PrintStream.println:(Ljava/lang/St
ring;)V
   //---------------------------------------------------------------------------------------------
   265: return

}

测试得到类似如下的一组结果：

#1

invokevirtual:   250

invokespecial:   219

invokestatic:    125

invokeinterface: 1062

#2

invokevirtual:   281

invokespecial:   250

invokestatic:    141

invokeinterface: 1078
...
可以看出，静态方法调用最快，而通过接口调用方法最慢（比invokevirtual慢了3-4倍），调用private的方法比调用一般的方法稍快。

调用超类（在现在的jvm spec中与以前的有所不同，不是通过invokespecial来调用）的方法不是很好测试，再想想看。