1. package declaration (optional)
2. import statements (optional)
3. class or interface declaration

• java.lang -- not required to import
• java.awt
• java.applet
• java.net
• java.io
• java.util

• compile: javac xxx.java --- generate one or more class files
• run: java xxx -- interpret a class file with main() method

• "//" for a single line.
• "/*" .... "*/" for one or multiple lines.
• "/**" ... "*/" for document comments.

• constructors.
• member variables (static or instance)
• member methods (static or instance)
• floating code blocks (instance or static)

Note: class variable or class method means static variable or static method.

• if, if/else
• switch (case, default
• for
• while
• do/while
• break, continue, lable:statement

• local variable: defined inside a method or a block. (other names: automatic or temporary, or stack variables)
• instance variable: defined as a member, belonged to an individual instance of a class.
• class variable or static variable: defined as a member, shared among all instances of a class

• syntax:

  int [] i1; 
  int i2[];
  int i3[] = {1,2,3,4,5};
  

• create an array: use new.
• initialization: default values applied automatically.
• object array: Myclass[] mc = new Myclass[5];
• determine number of elements in an array:

  int[] ary = new int[5];
  int len = ary.length;//len = 5;
  

• access an element of array:

  int s = num[idx];
  

• two-dimentional array:

  int [][] i = new int[2][4];
  

• multi-dimentional array
• array copy:

  System.arraycopy(src,stPos, des, stPos, src.length);