1. Why is the following code not compile? Where is wrong?
The system provides a method of custom, the system no longer cause provide a default constructor. Resulting in code compiler can not pass.
What next 2 code output is?
package text1;
public class InitializeBlockClass {
{
field = 200;
}
public int field = 100;
public InitializeBlockClass(int value){
this.field = value;
}
public InitializeBlockClass(){
}
public static void main(String[] args) {
// TODO Auto-generated method stub
InitializeBlockClass obj = new InitializeBlockClass();
System.out.println(obj.field);
obj = new InitializeBlockClass(300);
System.out.println(obj.field);
}
}
Java field initialized law:
1. When performing the specified class member define default or initialization block type, a top surface of which which is executed first.
2. Perform class constructor.
3. Run TestStaticInitializeBlock.java example, look at the output, concludes that "static initialization block execution order."
Root class
{
static {
System.out.println ( "Root static initialization block");
}
{
System.out.println ( "normal initialization block the Root");
}
public Root ()
{
System.out.println ( " Root no argument constructor ");
}
}
class Mid the extends Root
{
static {
System.out.println (" Mid static initialization block ");
}
{
System.out.println (" Mid general initialization block ") ;
}
public Mid ()
{
System.out.println ( "Mid no argument constructor");
}
public Mid (String MSG)
{
// call the same class constructor overloads by the this
the this ();
the System .out.println ( "Mid constructor parameters with which parameter values:"+ msg);+ msg);
}
}
Class Leaf the extends Mid
{
static {
System.out.println ( "Leaf static initialization block");
}
{
System.out.println ( "Leaf normal initialization block");
}
public Leaf ()
{
// the super call the parent class has a constructor parameter string of
super ( "Java initialization sequence demo");
System.out.println ( "Leaf performed constructor");
}
}
public class TestStaticInitializeBlock
{
public static void main (string [ ] args)
{
new new Leaf ();
}
}
Static initialization block execution order:
1. static initialization block is executed only once.
2. Create a sub-type of the object, it will lead to the implementation of static initialization block of the parent type.
4. Static method only allows access to static data, then, how in a static method access instance members of the class (ie no additional field or method static keyword)?
{class Jingtai public
public int X = 200 is;
public static int Y = 300;
public static void Method ()
{
System.out.println ( "instance variables x =" + new jingtai () x.); // the class static method access instance variables in the class
System.out.println ( "static variable = Y" + Y);
}
public static void main (String [] args) {
Jingtai .method ();
Jingtai Jingtai EX = new new ();
System.out.println ( "X =" + ex.x);
}
}
Examples of the access member in a static method needs for the implementation of the constructor of the class dependent class instance object before.
Class static methods or properties, the essence is not a member of the class, in the java virtual machine installed at the time of the class, these things have a static object, it is only in this class, "the stranger", without going through the class constructor (the constructor) implementation example of the class; not static property or method, the loading of the class is not present, is intended for dependent class after performing a constructor for the class instance of the object exists.