Overloading and overriding method call

May 15, 2012 by Guoliang, 4 views

Overloading method will be determined by reference type, but override method will be determined by the actual object tyep.
property is determined by reference type too. 

package newjob.guoliang.corejava;

public class ReferenceTypeTest {
	public static void main(String[] args) {
		AClass a = new BClass();
		new ReferenceTypeTest().printClassDesc(a);
	}

	protected void printClassDesc(AClass a) {
		System.out.println("A_" + a.desc);
	}

	protected void printClassDesc(BClass b) {
		System.out.println("B_" + b.desc);
	}

}

class AClass {
	String desc = "ClassA";
}

class BClass extends AClass{
	String desc = "ClassB";
}

Output is:

A_ClassA
MethodClassB_ClassB

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Java method invoked sequence

May 15, 2012 by Guoliang, 2 views

Static block / variable;

Instance block / variable;

Constructor;

public class StaticTest {
	public static void main(String[] args) {
		// System.out.println(B.a);
		// System.out.println(C.c);
		StaticTest staticTest = new StaticTest();
		staticTest.printName();
	}

	static {
		System.out.println("Static_block_Main");
	}

	public StaticTest() {
		System.out.println("Consturctor_Main");
	}

	private void printName() {
		System.out.println("InstanceMethod");
	}
	{
		System.out.println("Instance_block_Main");
	}

}

Output is:

Static_block_Main
Instance_block_Main
Consturctor_Main
InstanceMethod

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About Java static block

May 15, 2012 by Guoliang, 4 views 
package scjp.liguoliang.com;

/**
 * I'm try to see the static block run rules,
 * B extends A, A has a static a, when we use B.a, class B did not loaed, just Class A loaded.
 * If B also has a static a, A and B will be loaded.
 * If a is finle, A and B will not be loaded both.
 * @author Li Guoliang
 *
 */
public class TestClassLoading {
	public static void main(String[] args) {
		System.out.println(B.a);
		System.out.println(C.c);
	}
}

class A {
	static String a = "A.a"; // how about if this is final
	static {
		System.out.println("Static_A_Class");
	}

	{
		System.out.println("Instance_A");
	}
}

class B extends A{
	// static String a = "B.a";
	static {
		System.out.println("Static_B_Class");
	}
}

/**
 * This class is designed for test the squence of static variable and block.
 * They run by the sequence of the code.
 * @author Li Guoliang
 *
 */
class C {

	static {
		System.out.println("Static_C");
	}
	static C c = new C();

	public C() {
		System.out.println("Constructor_C");
	}
}

Output

Static_A_Class
A.a
Static_C
Constructor_C
scjp.liguoliang.com.C@161f10f

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Which method will be called? about Overriding and Overloading in Java

May 13, 2012 by Guoliang, 5 views

Here are two class: Animal and Dog, Dog extends from Animal:

package scjp.liguoliang.com;

public class Animal {

	private String type = "Dog";
	public String name = "Animal";

	public String getType() {
		return type;
	}

	public void eat() {
		System.out.println(name + ", Animal eat...");
	}
}

package scjp.liguoliang.com;

public class Dog extends Animal {

	private String type = "Dog";
	public String name = "Dog";

	public String getType() {
		return type;
	}

	public void eat() {
		System.out.println(name + ", Dog eat...");
	}
}

And here is the test codes:

	public static void main(String[] args) {
		Dog dog = new Dog();
		Animal animalDog = new Dog(); // New dog, but type is Animal.

		System.out.println(dog.name);
		System.out.println(dog.getType());
		dog.eat();

		System.out.println(animalDog.name);
		System.out.println(animalDog.getType());
		animalDog.eat();

		System.out.println("\nWe are going to test overloading:");
		OverLoadingTest overLoadingTest = new OverLoadingTest();
		overLoadingTest.testEat(animalDog);
		overLoadingTest.testEat(dog);
	}

	public void testEat(Animal animal) {
		System.out.println("Test Animal eat");
	}

	public void testEat(Dog dog) {
		System.out.println("Test Dog eat");
	}

Here is the output:

Dog
Dog
Dog, Dog eat...
Animal // Get the property by reference Type, so print the name of ‘Animal’
Dog // Polymorphism, call the method of the instance in run time;
Dog, Dog eat...

We are going to test overloading:
Test Animal eat // Compiler will decide which method will be called by reference type when compiling. 
Test Dog eat

In summary:

1. overriding: Polymorphism is for instance method, so  an animal type reference to a dog Object will call dog’s method; but for properties, will use animals.

2. overloading: which method will be called has been determined when compiling by the reference type.

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Configuring the Apache Web Server to Run Perl 在Apache中运行Perl

May 5, 2012 by Guoliang, 2 views

1. Install Perl

2. Install Apache & config httpd：

Options Indexes FollowSymLinks
Add ExecCGI to this line. The line should now look like the following:
Options Indexes FollowSymLinks ExecCGI
Next, search for the following:
#AddHandler cgi-script .cgi
Uncomment this line by removing the # in front of the line, and add a .pl to the end of the line. The new line should look like this:
AddHandler cgi-script .cgi .pl

3. Start the server, and check the server environment:

http://localhost:8080/cgi-bin/printenv.pl

There should be some  environment variables like  DOCUMENT_ROOT/PATH/SCRIPT_FILENAME….

4. Drop a Perl(hello.pl) into the server：

#!D:/perl/bin/perl.exe
print "Content-type: text/html; charset=utf-8\n\n";
print "<phtml><head><title>Learning Perl</title></head><body>";
print "<h1>PerlPage</h1>";
print "<form action='upload.pl' method='post'>";
print "<input type=file name=='file'>";
print "<input type=text name='comment' size=20 value=''>";
print "<input type=submit name=enter value='Upload'>";
print "<form>";
print "</body></html>";

you can just drop this file in your ApacheHome/cgi-bin or your site if you have configured the httpd.conf;

5. check the Perl page:

http://localhost:8080/cgi-bin/hello.pl

 

Ref:http://www.editrocket.com/articles/perl_apache_windows.html

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