• Write code using the following methods of the java.lang.Math class: abs, ceil, floor, max, min, random, round, sin, COs, tan, sqrt.
• Describe the significance of the immutability of String objects.
• Describe the significance of wrapper classes, including making appropriate selections in the wrapper classes to suit specified behaviour requirements, stating the result of executing a fragment of code that includes an instance of one of the wrapper classes, and writing code using the following methods of the wrapper classes (e.g., Integer, Double, etc.):
  • doubleValue
  • floatValue
  • intValue
  • longValue
  • parseXxx
  • getXxx
  • toString
  • toHexString

The java.lang.* Packages

java.lang.Object

• ultimate ancestor of all java classes (if a class doesn't explicitly 'extend' another, then java makes it extend Object)
• inherited methods
  • wait(), notify(), notifyAll()
  • should override: boolean equals(Object that) (in object class is just ==, so only if refer to same object) and String toString() (in object class simply is the reference value)

java.lang.Math

• class is final (therefore can't extend it)
• constructor is private (therefore can't create an instance)
• all methods and constants are static
• constants: Math.PI, Math.E
• methods:
  • public static int abs(int i) - also for long, float, double
  • public static double ceil(double d) - smallest integer not less than d
  • public static double floor(double d) - largest integer not greater than d
  • public static int max(int i, int j) - also for long, float, double
  • public static int min(int i, int j) - also for long, float, double
  • public static double random() - >= 0.0 and <1.0
  • public static int round(float f)
  • public static long round(double d)
  • public static double sin(double rads) - also cos, tan, sqrt, pow

The Wrapper Classes

• are final
• Boolean, Byte, Short, Character, Integer, Long, Float, Double
• contains immutable value
• constructors:

  e.g.

  int i = 321; Integer wrappedInt = new Integer(i);, or new Integer(321) or Integer wrappedInt = new Integer("321"); ensure float string includes and 'f', and boolean is "True" or "False" (actually just checks for .equalsIgnoreCase("true"), otherwise sets it's value to false), and Float and Double can have +/-Infinity|NaN too can't do this way for a char all but Boolean can throw a NumberFormatException (a runtime exception)

• extraction: byteValue(), shortValue(), intValue(), longValue(), floatValue(), doubleValue(), called by any wrapped number, returns a byte, short, int, long, float, double primitive respectively
• characterInstance.charValue() returns a char, and booleanInstance.booleanValue() returns a boolean
• valueOf(String s)
  • static method for all wrapper classes except Character
  • returns the wrapped version
  • e.g. Integer wrappedInt = Integer.valueOf("321");
• static Byte|Short|Integer|Long|Float|Double.parseByte|Short|Int|Long|Float|Double(String s)
  • static method
  • returns the primitive
  • e.g. int i = Integer.parseInt("321");
  • can throw a NumberFormatException
• getBoolean|Integer|Long(String name_of_system_property)
  • static method
  • returns the wrapped value
  • overloaded getInteger|Long(String name_of_system_property, int|long default_value)
• all have good toString() and equals(Object that) methods
• static Integer|Long.toBinary|Octal|HexString(int|long)

java.lang.String

• immutable - so String literal added to a pool of literals at compile time
• String s = "text"; - kept in pool of strings (so '==' seems to work on strings created in this way)
• String s = new String("text"); - makes a copy of the string during run-time (so new creates a unique copy, can put back in pool with s.intern();)
• non-static methods:
  • char charAt(int i)
  • int indexOf(char c) and int lastIndexOf(char c)
  • boolean startsWith(String that) and boolean endsWith(String that)
  • boolean equals(String that), boolean equalsIgnoreCase(String that) and int compareTo(String that)
  • String substring(int start_index), String substring(int start_index, int end_index, String trim(), String toUpper|LowerCase(), String concat(String that)
  • int length()
  • String toString() - returns the executing object