分别用一千万次循环来比较StringBuilder的三种删除方法所用时间
未避免偶然性,再循环一百次来比较总时间
--主类
public class StringBuilderRemove {
public long newProject;//重新创建对象循环一千万次所用时间
public long delete;//删除字符串循环一千万次所用时间
public long updateLength;//修改长度循环一千万次所用时间
public void test() {
//第一种,新创建一个对象
long startTimeA = System.currentTimeMillis();
StringBuilder sb = null;
for (int i = 1; i <= 10000000; i++) {
sb = new StringBuilder();
sb.append("AAAAAAA");
sb.append("BBBBBBB");
sb.append("CCCCCCC");
sb.append("DDDDDDD");
sb.append("EEEEEEE");
sb.append("FFFFFFF");
sb.append("GGGGGGG");
String a = sb.toString();
}
this.newProject = System.currentTimeMillis() - startTimeA;//new新对象所花时间
//第二种,删除字符串
long startTimeB = System.currentTimeMillis();
for (int i = 1; i <= 10000000; i++) {
sb.delete(0, sb.length());
sb.append("AAAAAAA");
sb.append("BBBBBBB");
sb.append("CCCCCCC");
sb.append("DDDDDDD");
sb.append("EEEEEEE");
sb.append("FFFFFFF");
sb.append("GGGGGGG");
String a = sb.toString();
}
this.delete = System.currentTimeMillis() - startTimeB;//删除字符串所花时间
//第三种,设置长度
long startTimeC = System.currentTimeMillis();
for (int i = 1; i <= 10000000; i++) {
sb.setLength(0);
sb.append("AAAAAAA");
sb.append("BBBBBBB");
sb.append("CCCCCCC");
sb.append("DDDDDDD");
sb.append("EEEEEEE");
sb.append("FFFFFFF");
sb.append("GGGGGGG");
String a = sb.toString();
}
this.updateLength = System.currentTimeMillis() - startTimeC;//修改字符串长度所花时间
}
--测试类
public class Main {
public static void main(String[] args) {
StringBuilderRemove sbr = new StringBuilderRemove();
long a = 0;
long b = 0;
long c = 0;
for (int i = 0; i < 100; i++) {
sbr.test();
a += sbr.newProject;
b += sbr.delete;
c += sbr.updateLength;
}
System.out.println(a);
System.out.println(b);
System.out.println(c);
}
}
运行结果:
168046
95123
93593
结论:可以明显看出,重新创建对象的方法是最慢的,删除字符串和设置长度的方法差别不大.
