Java中的基本数据类型默认值扩展

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);
}