JavaAutoboxing的优缺点
发布时间：2010/9/30 16:24:52 来源：城市学习网 编辑：ziteng
/**
*
* The Advantages and Traps of Autoboxing
*
* 优点：
* 1. 代码更简洁
* 2. 自动使用最优的转换代码（比如使用Integer.valueOf(int)，而不是使用new Integer(int)）
*
* 缺点:
* 1. 如果不注意，可能会导致错误
* 2. 如果不注意，可能会导致效率低下
* 3. 有时需要强制类型转换。
*
* 参考：http://javaeffective.wordpress.com/2010/05/21/the-advantages-and-traps-of-autoboxing/
*
*/
public class M {
public static void main(String[] args) {
// 导致错误
Long longValue1 = 99L;
System.out.println(longValue1.equals(99L)); // true
System.out.println(longValue1.equals(99)); // false
System.out.println(longValue1 == 99L); // true
System.out.println(longValue1 == 99); // true
long t1;
long t2;
// 导致效率低下
// 实验组 1
t1 = System.currentTimeMillis();
Long counter1 = 0L; // Long counter = 0; 会报错！！！
for (long i = 0; i < 100000000; i++) {
counter1++; // 等价于 Long.valueOf(counter1.longValue() + 1)
}
t2 = System.currentTimeMillis();
System.out.println("time1 = " + (t2 - t1)); // 1625
// 实验组 2
t1 = System.currentTimeMillis();
long counter2 = 0;
for (long i = 0; i < 100000000; i++) {
counter2++;
}
t2 = System.currentTimeMillis();
System.out.println("time2 = " + (t2 - t1)); // 297
// Integer : 1 + 2 = 3
// 需强制类型转换，否则调用printSum(long, long)
// 强制转换为 int也会调用printSum(long, long)
printSum((Integer) 1, (Integer) 2);
// Long1 : 1 + 2 = 3
printSum(1L, 2L);
// 需强制类型转换
// Long2 : 1 + 2 = 3
printSum((Long) 1L, (Long) 2L);
// Float : 1.0 + 2.0 = 3.0
printSum(1F, 2F);
// Double : 1.0 + 2.0 = 3.0
printSum(1D, 2D);
}
public static void printSum(long a, long b) {
System.out.println("Long1 : " + a + " + " + b + " = " + (a + b)); // true
}
public static void printSum(Long a, Long b) {
System.out.println("Long2 : " + a + " + " + b + " = " + (a + b)); // true
}
public static void printSum(Integer a, Integer b) {
System.out.println("Integer : " + a + " + " + b + " = " + (a + b)); // true
}
public static void printSum(Float a, Float b) {
System.out.println("Float : " + a + " + " + b + " = " + (a + b)); // true
}
public static void printSum(Double a, Double b) {
System.out.println("Double : " + a + " + " + b + " = " + (a + b)); // true
}
}
