[Java in NetBeans] Lesson 17. File Input/Output.

这个课程的参考视频和图片来自youtube。

    主要学到的知识点有：

We want to handle the bad Error. (e.g bad input / bugs in program)

1. File() : A Java representation of a file.

File file = new File("test.txt");

2. PrintWriter() : Write to a file. 

• Write string into the file. 

// Write 2 lines(Johnson, 26) into the test.txt file. (If not exist then create one, otherwise will overwrite it.)
PrintWriter output = new PrintWriter(file);
output.println("Johnson");
output.println("26");
output.close();

3. Scanner() : Read from a file. 

• Read string from the file. 

Scanner input = new Scanner(file);
String name = input.nextLine();
int age = input.nextLine();

4. Object Serialization : convert an object into a series of bytes so they can be written to disk 

• Serialization: Object to Disk
• Deserialization: Disk to Object
• In order to use the seialization, we need to add implement Serializable in the class definition (the contens will be in a binary format)

public class Student implements Serializable {

• FileInputStream & ObjectInputStream

　　     Read from a file as bytes and deserialize a data input stream back into an object

// deserialize the collection of students
FileinputStream fi = new FileinputSream(file);
ObjectInputStream input = new ObjectOutputStream(fi);
while(input.hasNext()){
    Student s =(Student) input.readObject();
    students.add(s);
}
input.close();// Important when writing a file as operating system will deny other programs access until the file is closed
fi.close();

• FileOutputStream & ObjectOutputStream

　　     Write to a file as bytes and serialize an object into a data input stream

// serialize the collection of students
FileOutputStream fo = new FileOutputSream(file);
ObjectOutputStream output = new ObjectOutputStream(fo);
for(Student s: students){
    output.writeObject(s);
}
output.close();// Important when writing a file as operating system will deny other programs access until the file is closed
fo.close();