Total Pageviews

Wednesday, June 4, 2014

Java/Android Notes

  • How is Java program created/built/executed?
    • Create
      • Create class Hello.
      • Inside the Hello class, create a static method main with the signature:
        • public static void main(String[] args)
      • Inside the main method, use System.out.println("Hello world!"); to write to standard output.
    • Use javac to create Hello.class.
    • Use java Hello to run Hello.class, notice no .class extension when using java to execute a class.
  • Write a Java program that defines/uses package.
    • Assume current directory is hello.
    • mkdir -p a/b/c && cd a/b/c
    • Inside a/b/c, create a file
    • Inside file, declare the package it belongs to:
      • package a.b.c;
    • Inside file, create a public class Add.
    • Inside class Add, create a public static method add with the signature:
      • public static int add(int a, int b)
    • Go back to hello directory: cd hello.
    • Create a file
    • Inside the file, import class Add from package a.b.c:
      • import a.b.c.Add;
    • Inside the file, create a public static main method with the signature:
      • public static void main(String[] args)
    • The main method:
      • Read arguments from the command line.
      • Use Integer.parseInt to convert them to int.
      • Call Add.add to compute the sum.
      • Call System.out.println to print the result to standard output.
    • In directory hello, compile the file by javac, it generates AddTest.class.
    • Run the program: java AddTest 1 2, should see the result 3 printed to the standard output.
  • Java's member access rule:
  • Modifier    | Class | Package | Subclass | World
    public      |  y    |    y    |    y     |   y
    protected   |  y    |    y    |    y     |   n
    no modifier |  y    |    y    |    n     |   n
    private     |  y    |    n    |    n     |   n
    y: accessible
    n: not accessible
  • How to import .jar in ADT
    • Download the library .jar file x to folder p.
    • In the `Package Explorer', find libs folder (if not exists, create one: New -> Folder).
    • Right click libs, Import -> General -> File System.
    • Navigate to folder p, find x in the right panel. Check the check-box. Click Finish.
    • If libs is already in the build path, we are done. Otherwise, Right click the project, Build Path -> Configure Build Path..., select Libraries tab. Click Add JARs..., find the x, click ok.
  • How to setup jni? (TODO)
  • How to call c/c++ procedure from Java through jni? (TODO)
  • How to call Java procedure from c/c++ through jni? (TODO)

No comments:

Post a Comment