为什么数字类上的valueOf / parse方法拒绝Java 7中的有效数字？

scala> java.lang.Float.valueOf(\"1_2_3.4_5_6\")
java.lang.NumberFormatException: For input string: \"1_2_3.4_5_6\"
    at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1242)
    at java.lang.Float.valueOf(Float.java:416)

scala> java.lang.Byte.valueOf(\"0b01010101\")
java.lang.NumberFormatException: For input string: \"0b01010101\"
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:492)
    at java.lang.Byte.parseByte(Byte.java:148)
    at java.lang.Byte.valueOf(Byte.java:204)
    at java.lang.Byte.valueOf(Byte.java:230)