测试下String和StringBuilder的效率

public class Test
{
public static void main (String args[]){
String str="";
long starTime=System.currentTimeMillis();
for(int i=0;i<10000;i++){
str+=i;
}
long endTime=System.currentTimeMillis();
long time=endTime-starTime;
System.out.println("String use time="+time);
StringBuilder builder=new StringBuilder("");
starTime=System.currentTimeMillis();
for(int j=0;j<10000;j++){
builder.append(j);
}
endTime=System.currentTimeMillis();
time=endTime-starTime;
System.out.println("StringBuilder use time="+time);

}
}