Swap I

1
Swap I

• class Swap
• public static void swap(int i, int j)
• int temp i
• i j
• j temp
• public static void swap(String s1, String s2)
  
• String temp s1
• s1 s2
• s2 temp

2
Swap II

• public static void swap(int data, int i, int j)
  
• int temp datai
• datai dataj
• dataj temp

3
Swap III

• public static void main(String args)
• int a 7, b8
• swap(a,b)
• System.out.println(a " " b)
• String s1 "hihihi", s2 "hahaha"
• swap(s1,s2)
• System.out.println(s1 " " s2)
• int a 0, 1 ,13, 32, 57
• swap(a, 1, 3)
• System.out.println(a1 " " a3)

4
Swap III

• public static void main(String args)
• int a 7, b8
• swap(a,b)
• System.out.println(a " " b)
• String s1 "hihihi", s2 "hahaha"
• swap(s1,s2)
• System.out.println(s1 " " s2)
• int c 0, 1 ,13, 32, 57
• swap(c, 1, 3)
• System.out.println(c1 " " c3)

5
Static fields I

• class NewTurtle
• private static int counter 0
• private int id
• NewTurtle()
• counter
• id counter
• //
• // other methods
• //

6
Static fields II

• parallelPaint()
• tailDown()
• turnLeft(id(360/counter)) // counter gt 0 (why
  ?)
• moveForward(100)
• public static void main(String args)
• NewTurtle turtles new NewTurtle6
• for (int i0 iltturtles.length i)
• turtlesi.parallelPaint()

7
Static fields II

• parallelPaint()
• tailDown()
• turnLeft(id(360/counter)) // counter gt 0 (why
  ?)
• moveForward(100)
• public static void main(String args)
• NewTurtle turtles new NewTurtle6
• for (int i0 iltturtles.length i)
• turtlesi new NewTurtle()
• turtlesi.parallelPaint()

8
Finalize method

• Called when the object is destructed.
• System.gc() causes the JVM to do maximal effort
  to reclaim space from discarded objects ASAP
• For NewTurtle
• finalize()
• --counter

9
Objects as fields of other classes I

• class BigInt
• boolean number
• BigInt(boolean number)
• this.number number
• public static String toString()
• String result ""
• for (int i 0 i lt number.length i)
• result numberi ? '1' '0'
• return result

10
Objects as fields of other classes I

• class BigInt
• boolean number
• BigInt(boolean number)
• this.number number
• public String toString()
• String result ""
• for (int i 0 i lt number.length i)
• result numberi ? '1' '0'
• return result

11
Objects as fields of other classes II

• public static void main(String args)
• boolean number false, false, false
• BigInt zero new BigInt(number)
• System.out.println(zero)
• number2 true
• BigInt one new BigInt(number)
• number1 true
• BigInt three new BigInt(number)
• System.out.println(zero)
• System.out.println(one)
• System.out.println(three)

12
Maze Traversal I

• We can use recursion to find a path through a
  maze
• From each location, we can search in each
  direction
• Recursion keeps track of the path through the
  maze
• The base case is an invalid move or reaching the
  final destination

13
Maze Traversal II

• public boolean traverse (int row, int column)
• boolean done false
• if (valid (row, column)) // checks the cell
  is not blocked, not
• //
  visited and inside the matrix
• gridrowcolumn TRIED // this cell
  has been tried
• if (row grid.length-1 column
  grid0.length-1)
• done true // the maze is solved
• else
• done traverse (row1, column)
  // down
• if (!done)
• done traverse (row, column1)
  // right

14
Maze Traversal III

• if (!done)
• done traverse (row-1, column)
  // up
• if (!done)
• done traverse (row, column-1)
  // left
• if (done) // this location is part of
  the final path
• gridrowcolumn PATH
• return done

15
Indirect Recursion

• A method invoking itself is considered to be
  direct recursion
• A method could invoke another method, which
  invokes another, etc., until eventually the
  original method is invoked again
• For example, method m1 could invoke m2, which
  invokes m3, which in turn invokes m1 again
• This is called indirect recursion, and requires
  all the same care as direct recursion
• It is often more difficult to trace and debug

16
Indirect Recursion