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  • 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);
    	}
    

      

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  • 原文地址:https://www.cnblogs.com/Rong-/p/5519489.html
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