Java API

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• java.lang.String
  • in default import package
  • e.g. "","Peter","city U", "Text", and "DNA"
  • is an array of char
• java.util.Arrays
  • a collection of components of the same type

    declarations

    int[] intArray; // delare intArray as an array of int

    creation of array object i.e. allocation of space for its components

    intArray = new int[7]; // allocate space for seven int

    array initializer

    comma-separated list of expressions, enclosed by braces "{" and "}" e.g. intArray = {1,2,3,4,5,6,7};

    accessing component of an array

    intArray[i] where i is in the range of 0 to intArray.length - 1 or else IndexOutOfBoundsException will be thrown

  • multidimensional array e.g. int[][] = {{1,2,3},null,{7,8,9}};
  • passing Array as argument e.g. public static void main(String[] args) {}
• 1 field, 11 constructors, about 60 methods, 8 methods inherited from java.lang.Object; and concatenation operator ( + )
  • an array of char is not a String i.e. they are different object (state, behavior, and identity)

    identity and value

    char[] charArray = {'a','d','a'};
    String name = "ada";

    behavior

    charArray.length;
    name.length();

    String object is immutable

    name.toCharArray(); and provision of StringBuffer class

  • StringClassDemo.java
• java.util.StringTokenizer
  • break string into token
  • "chan tai man_12345678_99" represent a students record of Name, ID, and Grade
  • '_' and space can be used as delimiter
  • StringTokenizerClassDemo
• The Wrapper Classes

  • primitive type	boolean	byte	short	int	long	char	float	double
    reference	Boolean	Byte	Short	Integer	Long	java.lang.Character	Float	Double
    conversion	Boolean.parseBoolean()	Byte.parseByte()	Short.parseShort()	Integer.parseInteger()	Long.parseLong()	Character.getNumericValue(char ch)	Float.parseFloat()	Double.parseDouble()

  • int i = 1;
    Integer j = new Integer(1);
    "i is not j"

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