您的基准测试是错误的。使用最新的Java 7和适当的预热，两种方法之间的区别非常大：
Person::main: estimatedSeconds 1 = '8,42'Person::main: estimatedSeconds 2 = '0,01'
这是完整的可运行代码：
import java.util.Calendar;import java.util.Date;import java.util.TimeZone;public class Person { private Date birthDate; static Date BOOM_START; static Date BOOM_END; public Person(Date birthDate) { this.birthDate = new Date(birthDate.getTime()); } static { Calendar gmtCal = Calendar.getInstance(TimeZone.getTimeZone("GMT")); gmtCal.set(1946, Calendar.JANUARY, 1, 0, 0, 0); BOOM_START = gmtCal.getTime(); gmtCal.set(1965, Calendar.JANUARY, 1, 0, 0, 0); BOOM_END = gmtCal.getTime(); } public boolean isBabyBoomerWrong() { // Unnecessary allocation of expensive object Calendar gmtCal = Calendar.getInstance(TimeZone.getTimeZone("GMT")); gmtCal.set(1946, Calendar.JANUARY, 1, 0, 0, 0); Date boomStart = gmtCal.getTime(); gmtCal.set(1965, Calendar.JANUARY, 1, 0, 0, 0); Date boomEnd = gmtCal.getTime(); return birthDate.compareTo(boomStart) >= 0 && birthDate.compareTo(boomEnd) < 0; } public boolean isBabyBoomer() { return birthDate.compareTo(BOOM_START) >= 0 && birthDate.compareTo(BOOM_END) < 0; } public static void main(String[] args) { Person p = new Person(new Date()); for (int i = 0; i < 10_000_000; i++) { p.isBabyBoomerWrong(); p.isBabyBoomer(); } long startTime = System.nanoTime(); for (int i = 0; i < 10_000_000; i++) { p.isBabyBoomerWrong(); } double estimatedSeconds = (System.nanoTime() - startTime) / 1000000000.0; System.out.println(String.format("Person::main: estimatedSeconds 1 = '%.2f'", estimatedSeconds)); startTime = System.nanoTime(); for (int i = 0; i < 10_000_000; i++) { p.isBabyBoomer(); } estimatedSeconds = (System.nanoTime() - startTime) / 1000000000.0; System.out.println(String.format("Person::main: estimatedSeconds 2 = '%.2f'", estimatedSeconds)); }}
