为了进行基准测试，我使用 LFSR 生成器编写了一个测试程序，以防止编译器优化测试数组。无法下载 pjc，但我认为时间应该类似于 Tom 的 IntBuffer 课程，这是迄今为止的赢家。 ByteArrayOutputStream 方法与我原来的ArrayList<Integer> 方法的速度差不多。我在 3GHz Pentium 4 上运行 J2SE 6u13，大约 220 值，在 JIT 运行之后，IntBuffer 方法大约需要 40 毫秒（每个项目只需 40 纳秒！）使用“健忘”集合的参考实现，该集合仅将最后一个参数存储到visit()（因此编译器不会对其进行优化）。其他两种方法大约需要 300 毫秒，大约慢 8 倍。
编辑：我怀疑 Stream 方法的问题是我必须捕获的潜在异常，不确定。
（对于参数运行 PrimitiveArrayTest 1 2）
package com.example.test.collections;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class PrimitiveArrayTest {
interface SomeObject {
public int getX();
}
interface Visitor {
public void visit(SomeObject obj);
}
public static class PlainObject implements SomeObject
{
private int x;
public int getX() { return this.x; }
public void setX(int x) { this.x = x; }
}
public static class Thing
{
/* here's a LFSR
* see http://en.wikipedia.org/wiki/Linear_feedback_shift_register
* and http://www.ece.cmu.edu/~koopman/lfsr/index.html
*/
private int state;
final static private int MASK = 0x80004;
private void _next()
{
this.state = (this.state >>> 1)
^ (-(this.state & 1) & MASK);
}
public Thing(int state) { this.state = state; }
public void setState(int state) { this.state = state; }
public void inviteVisitor(Visitor v, int terminationPoint)
{
PlainObject obj = new PlainObject();
while (this.state != terminationPoint)
{
obj.setX(this.state);
v.visit(obj);
_next();
}
}
}
static public abstract class Collector implements Visitor
{
abstract public void initCollection();
abstract public int[] getCollection();
public int[] extractX(Thing thing, int startState, int endState)
{
initCollection();
thing.setState(startState);
thing.inviteVisitor(this, endState);
return getCollection();
}
public void doit(Thing thing, int startState, int endState)
{
System.out.printf("%s.doit(thing,%d,%d):\n",
getClass().getName(),
startState,
endState);
long l1 = System.nanoTime();
int[] result = extractX(thing,startState,endState);
long l2 = System.nanoTime();
StringBuilder sb = new StringBuilder();
sb.append(String.format("%d values calculated in %.4f msec ",
result.length, (l2-l1)*1e-6));
int N = 3;
if (result.length <= 2*N)
{
sb.append("[");
for (int i = 0; i < result.length; ++i)
{
if (i > 0)
sb.append(", ");
sb.append(result[i]);
}
sb.append("]");
}
else
{
int sz = result.length;
sb.append(String.format("[%d, %d, %d... %d, %d, %d]",
result[0], result[1], result[2],
result[sz-3], result[sz-2], result[sz-1]));
}
System.out.println(sb.toString());
}
}
static public class Collector0 extends Collector
{
int lastint = 0;
@Override public int[] getCollection() { return new int[]{lastint}; }
@Override public void initCollection() {}
@Override public void visit(SomeObject obj) {lastint = obj.getX(); }
}
static public class Collector1 extends Collector
{
final private List<Integer> ints = new ArrayList<Integer>();
@Override public int[] getCollection() {
int N = this.ints.size();
int[] array = new int[N];
int j = 0;
for (Integer i : this.ints)
{
array[j++] = i;
}
return array;
}
@Override public void initCollection() { }
@Override public void visit(SomeObject obj) { ints.add(obj.getX()); }
}
static public class Collector2 extends Collector
{
/*
* adapted from http://stackoverflow.com/questions/1167060
* by Tom Hawtin
*/
private int[] values;
private int size = 0;
@Override public void visit(SomeObject obj) { add(obj.getX()); }
@Override public void initCollection() { values = new int[32]; }
private void add(int value) {
if (!(this.size < this.values.length)) {
this.values = java.util.Arrays.copyOf(
this.values, this.values.length*2);
}
this.values[this.size++] = value;
}
@Override public int[] getCollection() {
return java.util.Arrays.copyOf(this.values, this.size);
}
}
static public class Collector3 extends Collector
{
/*
* adapted from http://stackoverflow.com/questions/1167060
* by Tom Hawtin
*/
final ByteArrayOutputStream byteOut = new ByteArrayOutputStream();
final DataOutputStream out = new DataOutputStream(this.byteOut);
int size = 0;
@Override public int[] getCollection() {
try
{
this.out.flush();
final int[] ints = new int[this.size];
final ByteArrayInputStream byteIn
= new ByteArrayInputStream(this.byteOut.toByteArray());
final DataInputStream in = new DataInputStream(byteIn);
for (int ct=0; ct<ints.length; ++ct) {
ints[ct] = in.readInt();
}
return ints;
}
catch (IOException e) { /* gulp */ }
return new int[0]; // failure!?!??!
}
@Override public void initCollection() { }
@Override public void visit(SomeObject obj) {
try {
this.out.writeInt(obj.getX());
++this.size;
}
catch (IOException e) { /* gulp */ }
}
}
public static void main(String args[])
{
int startState = Integer.parseInt(args[0]);
int endState = Integer.parseInt(args[1]);
Thing thing = new Thing(0);
// let JIT do its thing
for (int i = 0; i < 20; ++i)
{
Collector[] collectors = {new Collector0(), new Collector1(), new Collector2(), new Collector3()};
for (Collector c : collectors)
{
c.doit(thing, startState, endState);
}
System.out.println();
}
}
}