在我的简单测试中，Java在递归算法速度比较上胜过c++

使用这种分治算法(Programming Pearls p80)找到数组中任何相邻子向量的最大和，Java程序比在Win7 x64上使用8GB RAM测试的c++程序要快。

Java和c++都运行在一个CPU内核上。

在JVM上做了什么样的优化来实现这一点?

JVM 1使用:

Java版本"1.6.0_21"
Java(TM) SE Runtime Environment (build 1.6.0_21-b07)
Java HotSpot(TM) 64位服务器VM (build 17.0-b17，混合模式)
虚拟机参数-Xmx12000m

JVM 2已使用:jrockit-jdk1.6.0_24-R28.1.3-4.0.1
虚拟机参数-Xmx12000m

Visual Studio 2008 x64自带的默认Microsoft编译器

乘以 :

 //Java JVM 1, Oracle JRE
 //0x1fffffff: about 38s, sum 144115187270549505
 //0x2fffffff: about 56s, sum 324259171962716161
 //0x3fffffff: about 81s, sum 576460750692810753
 //Java JVM 2, Oracle JRockit jrockit-jdk1.6.0_24-R28.1.3-4.0.1
 //0x1fffffff: about 46s
 //0x2fffffff: about 69s
 //0x3fffffff: about 95s     
 //Cpp
 //0x1fffffff: around 45s, x64 Release
 //0x2fffffff: around 68s, x64 Release sum: 324259171962716161
 //0x3fffffff: around 93s, x64 Release sum: 576460750692810753, 

final int MAX = 0x3fffffff; 
Pearls1 pearls1 = new Pearls1();
pearls1.arr = new int[MAX];
for (int i = 0; i < MAX; i++)
{
    pearls1.arr[(int) i] = i;                
}
long startTime = System.nanoTime();
long sum = pearls1.binaryForce(0, MAX - 1);
long endTime = System.nanoTime();
long binaryForce(long lower, long upper) {
    //std::cout << "binaryForce("<< lower << ","<< upper <<")" << std::endl;
    if( lower > upper ) {
        return 0;
    } 
    if( lower == upper ) {      
        return Math.max( 0L, arr[(int) lower] ) ;       
    }
    long middle = ( lower + upper ) /2 ;
    long lmax = 0,  sum = 0;
    for( long i = middle; i >=lower; i-- ) {
        sum += arr[(int) i];        
        lmax = Math.max( lmax, sum);
    }
    long rmax = 0;
    sum = 0;
    //for( long i = middle+1; i <= upper; i++ ) {
    for( long i = upper; i > middle; i-- ) {
        sum += arr[(int) i];
        rmax = Math.max(rmax, sum);     
    }
    long theMax = lmax+rmax;
    long binarySumLeft = binaryForce(lower, middle);
    long binarySumRight = binaryForce(middle+1, upper);
    if( theMax > binarySumLeft && theMax > binarySumRight ) {
        return theMax;
    }
    else if( binarySumLeft > theMax && binarySumLeft > binarySumRight ) {
        return binarySumLeft;
    }
    else if ( binarySumRight > theMax && binarySumRight > binarySumLeft ) {
        return binarySumRight;
    }
    else {
        return theMax;      
    }
}

 int main(...) {
    MAX = 0x3fffffff;
    arr = new long[MAX];
    for( long i=0;i<MAX;i++) {
        //arr[i] = rand();
        arr[i] = i;
    }
    timeb startTime, endTime;
    ftime( &startTime);
    std::cout << "Start time: " << startTime.time << " sec, " << startTime.millitm << " ms" << std::endl;
    sum = binaryForce(0, MAX-1);
    std::cout << "sum: " << sum <<std::endl;
    ftime( &endTime);
    std::cout << "End time: " << endTime.time << " sec, " << endTime.millitm << " ms" << std::endl;
    long runTimeSec = endTime.time - startTime.time;
    long runTimeMs = endTime.millitm - startTime.millitm;
    std::cout << "Run time: " << runTimeSec << " sec, " << runTimeMs << " ms" << std::endl;
 }
long long binaryForce(long lower, long upper) {
    //std::cout << "binaryForce("<< lower << ","<< upper <<")" << std::endl;
    if( lower > upper ) {
        return 0;
    } 
    if( lower == upper ) {        
        return std::max( 0L, arr[lower] ) ;        
    }
    long middle = ( lower + upper ) /2 ;
    long long lmax = 0,  sum = 0;
    for( long i = middle; i >=lower; i-- ) {
        sum += arr[i];        
        lmax = std::max( lmax, sum);
    }
    long long rmax = 0;
    sum = 0;
    //for( long i = middle+1; i <= upper; i++ ) {
    for( long i = upper; i > middle; i-- ) {
        sum += arr[i];
        rmax = std::max(rmax, sum);        
    }
    long long theMax = lmax+rmax;
    long long binarySumLeft = binaryForce(lower, middle);
    long long binarySumRight = binaryForce(middle+1, upper);
    if( theMax > binarySumLeft && theMax > binarySumRight ) {
        //std::cout << arr[theMax] << std::endl;
        return theMax;
    }
    else if( binarySumLeft > theMax && binarySumLeft > binarySumRight ) {
        //std::cout << arr[binarySumLeft] << std::endl;
        return binarySumLeft;
    }
    else if ( binarySumRight > theMax && binarySumRight > binarySumLeft ) {
        //std::cout << arr[binarySumRight] << std::endl;
        return binarySumRight;
    }
    else {
        //std::cout << arr[theMax] << std::endl;
        return theMax;        
    }
}