是否有任何负面的创造巨大的字符串？例如,如果我们从一个潜在的巨大的文本文件中读取文本：
while (scanner.hasNext()) {
someString += scanner.next();
}
// do something cool with someString
谢谢
解决方法
流媒体vs不
当您可以流式传输时,您可以处理任何大小的文件(假设您真的可以忘记所有已经看到的数据).你最终会有一个自然的O(n)复杂性,这是一件非常好的事情.你不会因为内存不足而中断.
流式可爱…但在每种情况下都不起作用.
StringBuilder的
似乎对StringBuilder建议有一定的争议,这里是显示效果的基准.我不得不减小基准的大小,以便在合理的时间内慢速版本甚至完成.
结果先,然后代码.这是一个非常粗糙和准备的基准,但结果足够戏剧性,使得点…
c:\Users\Jon\Test>java Test slow Building a string of length 120000 without StringBuilder took 21763ms c:\Users\Jon\Test>java Test fast Building a string of length 120000 with StringBuilder took 7ms
和代码…
class FakeScanner
{
private int linesLeft;
private final String line;
public FakeScanner(String line,int count)
{
linesLeft = count;
this.line = line;
}
public boolean hasNext()
{
return linesLeft > 0;
}
public String next()
{
linesLeft--;
return line;
}
}
public class Test
{
public static void main(String[] args)
{
FakeScanner scanner = new FakeScanner("test",30000);
boolean useStringBuilder = "fast".equals(args[0]);
// Accurate enough for this test
long start = System.currentTimeMillis();
String someString;
if (useStringBuilder)
{
StringBuilder builder = new StringBuilder();
while (scanner.hasNext())
{
builder.append(scanner.next());
}
someString = builder.toString();
}
else
{
someString = "";
while (scanner.hasNext())
{
someString += scanner.next();
}
}
long end = System.currentTimeMillis();
System.out.println("Building a string of length "
+ someString.length()
+ (useStringBuilder ? " with" : " without")
+ " StringBuilder took " + (end - start) + "ms");
}
}
