将值传递给java中的成员变量

Question

Why can we do this:

class A{int a=5;}

but are not allowed to do this:

class A {
     int a;
     a=5;       
}

Answer 1

just put it inside a block then.

class A {
     int a;
     {a=5;}       
}

An initialization block will run every time you make in instance of the class eg

new A();

this is of course between two other initializations related to creating a new instance. first is the field's initializations like when you declare a field with a value.

int a = 25;

then the block initialization

{
  a = 5;
}

then the constructor:

A() {
    a = 6;
}