标签：java i++ static blog 创建 instance end 创建ca object c
String s = new String("stringette"); // DON‘T DO THIS!
The improved version is simply the following:
String s = "stringette";
根据生日来判断是否是婴儿潮时期出生的，isBabyBoomer()是一个糟糕的设计，每次调用这个方法都会创建Calendar,TimeZone以及2个Date对象实例，当此方法被频繁调用时将会非常地影响性能。
public class Person { private final Date birthDate; // DON‘T DO THIS! public boolean isBabyBoomer() { // 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; } }
这个是优化后的方法，The improved version of the Person class creates Calendar, TimeZone, and Date instances only once
这些对象都是初始化后不会再被修改
class Person { private final Date birthDate; /** * The starting and ending dates of the baby boom. */ private static final Date BOOM_START; private static final Date BOOM_END; 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 isBabyBoomer() { return birthDate.compareTo(BOOM_START) >= 0 && birthDate.compareTo(BOOM_END) < 0; } }
autoboxing(自动装箱)也会带来非常大的性能影响
// Hideously slow program! Can you spot the object creation? public static void main(String[] args) { Long sum = 0L; for (long i = 0; i < Integer.MAX_VALUE; i++) { sum += i; } System.out.println(sum); }
Java之创建对象>5.Avoid creating unnecessary objects
标签：java i++ static blog 创建 instance end 创建ca object c
原文地址：http://www.cnblogs.com/frankyou/p/6913941.html
