Why does the first gender print out null
I"ve tried val gender: String = "male" , but the results don"t seem to be right.
constructor
zhu
null
derived constructor
zhu
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femalethere is a book suitable for this type of pit: " Scala Puzzle "
Chapter 4 inherits
the following rules control the initialization and overloading behavior ofval:
1. Superclasses are initialized before subclasses;
2. Members are initialized in the declared order;
3. When avalis overloaded, it can be initialized only once;
4. Similar to abstractval, overloadedvalhas a default initial value during superclass construction.
also says that you can use lazy val , but lazy val also has some disadvantages:
1. Due to the occurrence of Synchronize at the bottom, this will incur a slight performance cost;
2. The abstractlazy valcannot be declared;
3. Usinglazy valis easy to generate circular references, resulting in stack overflow errors and even deadlocks on the first visit.
4. Deadlocks can occur if a declaration is made between objects and the circular dependency betweenlazy valdoes not exist, which may be very subtle and imperceptible.
in addition, there are two other methods, one is to change val to def , and the other is to preinitialize the field, as follows:
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