effictive - 불필요한 개체 생성 방지

demo01:

package com.xiaohao.effective;

import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;

/**
 *  Calendar，BOOM_START，BOOM_END
 * @author Administrator
 *
 */
public class Demo01 {
	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 static boolean isBabyBoomer(Date birthDate) {
		return birthDate.compareTo(BOOM_START) >= 0 &&
				birthDate.compareTo(BOOM_END) < 0;
	}
}

demo02:

package com.xiaohao.effective;

import java.util.Date;
/**
 * countNum01 sum +=1, sum = sum + 1, sum ， “+” ， sum
 *  ，sum = sum.intValue() + 1; Long sum = new Long(sum);
 *  Long ，  ,  countNum02 。
 *  ： ， 
 * @author Administrator
 *
 */
public class Demo02 {
	private static Demo02 d= new Demo02();
	
	public static void countNum01(){
		Long sum = 0L;
		long t1 = new Date().getTime();
		for(long i=0;i

데모 02 테스트:

package com.xiaohao.test;

import org.junit.Test;

import com.xiaohao.effective.Demo02;

public class TestEffective {
	
	@Test
	public void testDemo02() {
		Demo02.getInstance().countNum01();
		
		Demo02.getInstance().countNum02();
	}
}

output:
2305843005992468481 :case 7277 2305843005992468481 :case 655