StringBuffer和StringBuilder之间的主要区别是什么?在决定其中任何一项时是否存在性能问题?
当前回答
StringBuilder(在Java5中引入)与StringBuffer相同,只是其方法不同步。这意味着它比后者具有更好的性能,但缺点是它不是线程安全的。
阅读教程了解更多详细信息。
其他回答
一个简单的程序说明了StringBuffer和StringBuilder之间的区别:
/**
* Run this program a couple of times. We see that the StringBuilder does not
* give us reliable results because its methods are not thread-safe as compared
* to StringBuffer.
*
* For example, the single append in StringBuffer is thread-safe, i.e.
* only one thread can call append() at any time and would finish writing
* back to memory one at a time. In contrast, the append() in the StringBuilder
* class can be called concurrently by many threads, so the final size of the
* StringBuilder is sometimes less than expected.
*
*/
public class StringBufferVSStringBuilder {
public static void main(String[] args) throws InterruptedException {
int n = 10;
//*************************String Builder Test*******************************//
StringBuilder sb = new StringBuilder();
StringBuilderTest[] builderThreads = new StringBuilderTest[n];
for (int i = 0; i < n; i++) {
builderThreads[i] = new StringBuilderTest(sb);
}
for (int i = 0; i < n; i++) {
builderThreads[i].start();
}
for (int i = 0; i < n; i++) {
builderThreads[i].join();
}
System.out.println("StringBuilderTest: Expected result is 1000; got " + sb.length());
//*************************String Buffer Test*******************************//
StringBuffer sb2 = new StringBuffer();
StringBufferTest[] bufferThreads = new StringBufferTest[n];
for (int i = 0; i < n; i++) {
bufferThreads[i] = new StringBufferTest(sb2);
}
for (int i = 0; i < n; i++) {
bufferThreads[i].start();
}
for (int i = 0; i < n; i++) {
bufferThreads[i].join();
}
System.out.println("StringBufferTest: Expected result is 1000; got " + sb2.length());
}
}
// Every run would attempt to append 100 "A"s to the StringBuilder.
class StringBuilderTest extends Thread {
StringBuilder sb;
public StringBuilderTest (StringBuilder sb) {
this.sb = sb;
}
@Override
public void run() {
for (int i = 0; i < 100; i++) {
sb.append("A");
}
}
}
//Every run would attempt to append 100 "A"s to the StringBuffer.
class StringBufferTest extends Thread {
StringBuffer sb2;
public StringBufferTest (StringBuffer sb2) {
this.sb2 = sb2;
}
@Override
public void run() {
for (int i = 0; i < 100; i++) {
sb2.append("A");
}
}
}
StringBuffer是线程安全的,但StringBuilder不是线程安全的。StringBuilder比StringBuffer更快。StringBuffer已同步,而StringBuilder未同步同步。
很好的问题
以下是我注意到的差异:
字符串缓冲区:-
StringBuffer is synchronized
StringBuffer is thread-safe
StringBuffer is slow (try to write a sample program and execute it, it will take more time than StringBuilder)
StringBuilder:-
StringBuilder is not synchronized
StringBuilder is not thread-safe
StringBuilder performance is better than StringBuffer.
常见问题:-
两者都有相同的方法和相同的签名。两者都是可变的。
StringBuffer已同步,StringBuilder未同步。
其他人正确地指出了两者之间的关键区别。然而,在性能方面,我想补充一点,JVM级别的优化“锁定Elision”可以使同步上下文中的性能差异几乎不存在。关于这一点的精彩阅读在这里和这里
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