我有一个关于使用 StringBuilder 的性能相关问题。
在一个很长的循环中,我正在操作 StringBuilder
并将其传递给另一个方法,如下所示:
for (loop condition) {
StringBuilder sb = new StringBuilder();
sb.append("some string");
. . .
sb.append(anotherString);
. . .
passToMethod(sb.toString());
}
在每个循环周期实例化 StringBuilder
是一个好的解决方案吗?像下面这样调用删除更好吗?
StringBuilder sb = new StringBuilder();
for (loop condition) {
sb.delete(0, sb.length);
sb.append("some string");
. . .
sb.append(anotherString);
. . .
passToMethod(sb.toString());
}
最佳答案
在我的迷你基准测试中,第二个大约快 25%。
public class ScratchPad {
static String a;
public static void main( String[] args ) throws Exception {
long time = System.currentTimeMillis();
for( int i = 0; i < 10000000; i++ ) {
StringBuilder sb = new StringBuilder();
sb.append( "someString" );
sb.append( "someString2"+i );
sb.append( "someStrin4g"+i );
sb.append( "someStr5ing"+i );
sb.append( "someSt7ring"+i );
a = sb.toString();
}
System.out.println( System.currentTimeMillis()-time );
time = System.currentTimeMillis();
StringBuilder sb = new StringBuilder();
for( int i = 0; i < 10000000; i++ ) {
sb.delete( 0, sb.length() );
sb.append( "someString" );
sb.append( "someString2"+i );
sb.append( "someStrin4g"+i );
sb.append( "someStr5ing"+i );
sb.append( "someSt7ring"+i );
a = sb.toString();
}
System.out.println( System.currentTimeMillis()-time );
}
}
结果:
25265
17969
请注意,这适用于 JRE 1.6.0_07。
根据 Jon Skeet 在编辑中的想法,这里是第 2 版。但结果相同。
public class ScratchPad {
static String a;
public static void main( String[] args ) throws Exception {
long time = System.currentTimeMillis();
StringBuilder sb = new StringBuilder();
for( int i = 0; i < 10000000; i++ ) {
sb.delete( 0, sb.length() );
sb.append( "someString" );
sb.append( "someString2" );
sb.append( "someStrin4g" );
sb.append( "someStr5ing" );
sb.append( "someSt7ring" );
a = sb.toString();
}
System.out.println( System.currentTimeMillis()-time );
time = System.currentTimeMillis();
for( int i = 0; i < 10000000; i++ ) {
StringBuilder sb2 = new StringBuilder();
sb2.append( "someString" );
sb2.append( "someString2" );
sb2.append( "someStrin4g" );
sb2.append( "someStr5ing" );
sb2.append( "someSt7ring" );
a = sb2.toString();
}
System.out.println( System.currentTimeMillis()-time );
}
}
结果:
5016
7516
关于java - 在循环中重用 StringBuilder 会更好吗?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/242438/