Basic Syntax and Concepts

• Java is case-sensitive

Variables

• Three types of variables

  • Fields - member variables in a class

  • Local variables - variables in a method or block of code

  • Parameters - variables in method declarations

    NOTE: No global variables in Java

• Data type

  • Primitive data type
    • boolean, byte, short, int, long, float, double, char
    • Overflow and underflow
    • BigDecimal class overcomes the precision issues of the floating number types
    • char in Java is 2 bytes to allow you to store Unicode characters
      • e.g. '\u0040' == 'A'
  • Class data type
  • Casting

• Declaration and Initialisation

• Literals

  • Good habit: add appropriate data type suffix

Operators

• Operator and operand
• Mathematical operators
  • Only overriding operator in Java: +, +=
    • Other data type variables will be automatically casted to a String
• Assignment operator
• Abbreviating operators
• ++, --
• Relational operators
• Logical operators
• Bitwise operators
• Ternary operator
• Casting operators
• ,
• Operator precedence

Expressions and Statements

• Expression is formed by combining variables, literals, method return values and operators

• Statement is an executable line or code block

  • Declaration statement

  • Expression statement

    • Assignment expressions
    • ++, --
    • Method calls
    • Object creation

  • Control flow statement

• Code organisation: whitespace and indentation

Flow control

• if-else
• switch
  • String can be used
  • Enhanced switch
• while
• do while
• for
• foreach

Method

• Function in Java

• Java method is pass-by-value

• A parameter is a variable in a method definition. When a method is called, the arguments are the data you pass into the method's parameters

• Method Overloading

  • Methods have the same name, but take a unique list of argument types
  • Overloaded methods CANNOT differ only by return type
  • Type promotion
    • Can cause compile time error if there are more than one methods matched

• Variable Arguments

  • Variable numbers of inputs

  • Must be the last parameter

  • void show(int... x) {
      for (int e : x)
        System.out.println(e);
    }
    
    // All valid
    show();
    show(10);
    show(10, 20);
    show(10, 20, 30);
    int[] x = {1, 2, 3};
    show(x);

• Command-line Arguments

  • String[] args in main()