Here is some simple java code .
class Test {
public static void main(final String[] args) {
TestClass c = new TestClass();
System.out.println(c.x);
}
}
class TestClass {
{
x = 2;
}
int x = 1;
}
I am getting the answer 1. Why? Is there no constructor used to initialize?
TestClass is compiled to be equivalent to this:
class TestClass {
{
this.x = 2;
}
int x;
{
this.x = 1;
}
}
The order of execution of initializer blocks, and variable initializer is specified in JLS § 12.5:
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:
[...]
4 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. [..]
So, the initializer blocks and variable initializers executed in order in which they appear in the source file. If you move the variable declaration, int x = 1;, before the initializer block, you'll get the result 2.
Technically, your Test class is compiled to the this:
class TestClass {
int x;
public TestClass() {
super();
x = 2;
x = 1;
}
}
For actual bytecode you can run javap -c command.
Because it would be compiled To :
class TestClass {
int x;
TestClass(){
this.x = 2;
this.x = 1;
}
}