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因为在很多情况下,如果要转换的数据为null,调用者期望的是返回默认值.
系统自动提供的默认值不能满足我们的需求,例如int的默认值为0,但是在sql查询中,如果查询失败,我们期望的是小于0的值,例如Select Count(1) from table1这样的操作.
为此,我提供了取得数据类型默认值的扩展函数
目标:
1)实现根据自己需要返回基本类型的默认值
2) 性能不要太差
1: 接口:
public static <T> T GetDefault(Class<T> t)
2: 实现
/**
* 获取数据类型的默认值
* @param t
* @return
*/
@SuppressWarnings("unchecked")
public static <T> T GetDefault(Class<T> t) {
if (t == Object.class) {
return null;
}
if (t == Integer.class) {
return t.cast(-1);
}
if (t == String.class) {
return t.cast("");
}
if (t == boolean.class) {
Object ret = false;
return (T)ret;
}
if (t == Boolean.class) {
Object ret = false;
return (T)ret;
}
if (t == BigDecimal.class) {
return (T)(new BigDecimal(-1));
}
Class<?> superClass = t.getSuperclass();
if (superClass == null) {
Object val = -1;
return (T)val;
}
if (t.getSuperclass().equals(Number.class)) {
Object val = -1;
return (T)val;
}
return null;
}
3: 测试代码
@Test
public void Test_HiTypeHelper_Cast() {
Integer val = 1;
int ret = HiTypeHelper.Cast(int.class, val);
Assert.assertEquals(ret, 1);
String text = "1";
ret = HiTypeHelper.Cast(int.class, text);
Assert.assertEquals(ret, 1);
text = "a";
ret = HiTypeHelper.Cast(int.class, text);
Assert.assertEquals(ret, -1);
int val2 = 1;
Integer ret2 = HiTypeHelper.Cast(Integer.class, val2);
Assert.assertEquals(ret2.intValue(), 1);
text = "1";
ret2 = HiTypeHelper.Cast(Integer.class, text);
Assert.assertEquals(ret2.intValue(), 1);
boolean bl = HiTypeHelper.Cast(boolean.class, 1);
Assert.assertTrue(bl);
bl = HiTypeHelper.Cast(boolean.class, 3);
Assert.assertTrue(bl);
bl = HiTypeHelper.Cast(boolean.class, 0);
Assert.assertFalse(bl);
bl = HiTypeHelper.Cast(boolean.class, -1);
Assert.assertFalse(bl);
bl = HiTypeHelper.Cast(boolean.class, "1");
Assert.assertTrue(bl);
bl = HiTypeHelper.Cast(boolean.class, "3");
Assert.assertTrue(bl);
bl = HiTypeHelper.Cast(boolean.class, "0");
Assert.assertFalse(bl);
bl = HiTypeHelper.Cast(boolean.class, "-1");
Assert.assertFalse(bl);
}
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原文地址：http://www.cnblogs.com/Rong-/p/5519489.html
