Java之创建对象>5.Avoid creating unnecessary objects详解编程语言

String s = new String("stringette"); // DON'T DO THIS!

String s = "stringette";

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; 
    } 
}

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; 
    } 
}

 // 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); 
}