这样做有什么区别？
public class SomeClass {
SomeObject obj = new SomeObject();
//rest of the code
}
和这个
public class SomeClass {
SomeObject obj;
public SomeClass(){
obj = new SomeObject();
}
//rest of the code
}
解决方法
根据Java语言规范第
12.5 Creation of New Class Instances章：
Just before a reference to the newly
created object is returned as the
result,the indicated constructor is
processed to initialize the new object
using the following procedure:
- Assign the arguments for the constructor to newly created parameter
variables for this constructor
invocation.- If this constructor begins with an explicit constructor invocation of
another constructor in the same class
(using this),then evaluate the
arguments and process that constructor
invocation recursively using these
same five steps. If that constructor
invocation completes abruptly,then
this procedure completes abruptly for
the same reason; otherwise,continue
with step 5.- This constructor does not begin with an explicit constructor
invocation of another constructor in
the same class (using this). If this
constructor is for a class other than
Object,then this constructor will
begin with an explicit or implicit
invocation of a superclass constructor
(using super). Evaluate the arguments
and process that superclass
constructor invocation recursively
using these same five steps. If that
constructor invocation completes
abruptly,then this procedure
completes abruptly for the same
reason. Otherwise,continue with step- Execute the instance initializers and instance variable initializers for
this class,assigning the values of
instance variable initializers to the
corresponding instance variables,in
the left-to-right order in which they
appear textually in the source code
for the class. If execution of any of
these initializers results in an
exception,then no further
initializers are processed and this
procedure completes abruptly with that
same exception. Otherwise,continue
with step 5. (In some early
implementations,the compiler
incorrectly omitted the code to
initialize a field if the field
initializer expression was a constant
expression whose value was equal to
the default initialization value for
its type.)- Execute the rest of the body of this constructor. If that execution
completes abruptly,then this
procedure completes abruptly for the
same reason. Otherwise,this procedure
completes normally.
所以区别只是一步(步骤4.或步骤5.),但结果是一样的.