【重新上本科】在实际问题中，内存赋值所拖累的效率（java版本）

继续上一篇博文《【重新上本科】在实际问题中，内存赋值所拖累的效率（c++版本）》。由于实际工作中同事的目标语言是java，所以我用相同的程序在java上面又尝试了一下。

先说下结论吧：有效率提升，不过提升幅度远小于在c++上面的效果。

代码如下：

public static void TestCopyingMemCost () throws IOException {
		int ARRAYSIZE = 10000000;
		// 1. create the fake data
		int [] pSource = new int [ARRAYSIZE];
		for (int i=0; i<ARRAYSIZE; i++)
		{
			if (0 == i%2)
				pSource[i] = i;
			else
				pSource[i] = ARRAYSIZE - i;
		}
		int [] pTmpBuf = new int [ARRAYSIZE];
		for (int i=0; i<ARRAYSIZE; i++)
			pTmpBuf[i] = 0;
		
		// 2. memory copy and compare, repeat n times
		long tBegin1 = System.nanoTime();
		double dCopyMemTotalClocks = 0.0;
		double dComparingTotalClocks = 0.0;
		for (int i=0; i<100; i++)
		{
			// 2.1 copy the values in memory
			long tBegin1_1 = System.nanoTime();
			int iTmpBufSize = 0;
			for (int j=0; j<ARRAYSIZE; j++)
			{
				if (0 == pSource[j]%3)
					pTmpBuf[iTmpBufSize++] = pSource[j];
			}
			long tEnd1_1 = System.nanoTime();
			dCopyMemTotalClocks += (double)(tEnd1_1 - tBegin1_1) / 1000000000;

			// 2.2 compare the items in temp buffer
			long tBegin1_2 = System.nanoTime();
			double dMax = -1.0;
			for (int k=0; k<iTmpBufSize; k++)
			{
				if (pTmpBuf[k] > dMax)
					dMax = pTmpBuf[k];
			}
			long tEnd1_2 = System.nanoTime();
			dComparingTotalClocks += (double)(tEnd1_2 - tBegin1_2) / 1000000000;
		}
		long tEnd1 = System.nanoTime();
		System.out.printf("Baseline time consuming %f\n", (double)(tEnd1 - tBegin1) / 1000000000);
		System.out.printf("copying memory time consuming %f\n", dCopyMemTotalClocks);
		System.out.printf("comparing value time consuming %f\n", dComparingTotalClocks);

		long tBegin2 = System.nanoTime();
		for (int i=0; i<100; i++)
		{
			double dMax = -1.0;
			for (int j=0; j<ARRAYSIZE; j++)
			{
				if (0 == pSource[i]%3)
				{
					if (pSource[i] > dMax)
						dMax = pSource[i];
				}
			}
		}
		long tEnd2 = System.nanoTime();
		System.out.printf("targeting time consuming %f\n", (double)(tEnd2 - tBegin2) / 1000000000);
	}

Baseline time consuming 5.693932
copying memory time consuming 5.099133
comparing value time consuming 0.594711

targeting time consuming 5.121151

完。

转载请注明出处：http://blog.csdn.net/xceman1997/article/details/20643471

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【重新上本科】在实际问题中，内存赋值所拖累的效率（java版本）

原文：http://blog.csdn.net/xceman1997/article/details/20643471