Introduction to Programming (Java) 3/12

Transcription

1 Introduction to Programming (Java) 3/12 Michal Krátký Department of Computer Science Technical University of Ostrava Introduction to Programming (Java) 2008/2009 c Michal Krátký Introduction to Programming (Java) 1/31

2 Statement Introduction to Programming (Java) 3/12 A statement is the expression finished by ; a = b + c ; / / an assignment statement i ++; sum( a, b ) ; / / a d e c l a r a t i o n statement i n t i ; double x, y, z ; / / a d e c l a r a t i o n and d e f i n i t i o n statement i n t i = 4 ; double x = , y, z = i 2. 0 ; c Michal Krátký Introduction to Programming (Java) 2/31

3 Block 1/2 Introduction to Programming (Java) 3/12 A block is a sequence of statements between braces and. Example: a = 2 7 ; i n t b = a / 3 ; / / b = 9 a = b % 2 ; / / a = 1 a = b / 2 ; / / a = 4 c Michal Krátký Introduction to Programming (Java) 3/31

4 Block 2/2 Introduction to Programming (Java) 3/12 A scope of a local variable declaration is from the point of the declaration to the end of the enclosed block. int a; a = 2 7 ; i n t b = a / 3 ; / / b = 9 a = b % 2 ; / / a = 1 a = b / 2 ; / / a = 4 / / here : a i s i n scope, b i s not v a l i d c Michal Krátký Introduction to Programming (Java) 4/31

5 1/4 An array is the static data structure including values of the same data types: homogeneous data structure the array size (length or the number of items) is known in the time of the array creation an identifier (the name of the array) is a reference at the array of values c Michal Krátký Introduction to Programming (Java) 5/31

6 2/4 double vector [ ] = new double [ 5 ] ; vector [ 0 ] = 1. 6 ; vector [ 1 ] = 2. 0 ; vector [ 2 ] = 0. 1 ; vector [ 3 ] = 1. 0 ; vector [ 4 ] = 1. 2 ; vector vector[0] vector[1] vector[2] vector[3] vector[4] An array is possible to initialize during the declaration (the new operator is called implicitly): double vector [ ] = 1. 6, 2. 0, 0. 1, 1. 0, 1. 2 ; c Michal Krátký Introduction to Programming (Java) 6/31

7 3/4 The index (the location of an item in an array) starts from 0 (the first item has the index 0). The last item in an array of the n size has the (n 1) index. The array includes the special attribute with the size of the array: i n t [ ] vector = new i n t [ 5 ] ; i n t n = v e ctor. l e n g t h ; The following declarations are equivalent: i n t [ ] vector ; i n t vector [ ] ; vector vector[0] vector[1] vector[2] vector[3] vector[4] c Michal Krátký Introduction to Programming (Java) 7/31

8 4/4 If the variable is declared as an array i n t [ ] a = new i n t [ 4 ] ; we call the a variable as the array. After an ansignment: i n t [ ] b = a ; a and b reference the same array. If we change the a[0] value, the b[0] value is changed as well. a b c Michal Krátký Introduction to Programming (Java) 8/31

9 , Example f i n a l i n t size = 3 1 ; i n t arraya [ ] = new i n t [ s ize ] ; i n t arrayb [ ] = arraya ; arraya [ 0 ] = 1 ; System. out. p r i n t l n ( " arraya [ 0 ] = " + arraya [ i ] + ", arrayb [ 0 ] = " + arrayb [ i ] ) ; c Michal Krátký Introduction to Programming (Java) 9/31

10 Multidimensional Multidimensional array is the one-dimensional array with arrays as items. double matrix [ ] [ ] = 1. 0, 0. 0, 0. 0, 0. 0, 0. 0, 1. 0, 0. 0, 0. 0, 0. 0, 0. 0, 1. 0, 0. 0 ; matrix [ 2 ] [ 2 ] = ; System. out. p r i n t l n ( " m a t r i x [ 2 ] [ 2 ] = " + m a t r i x [ 2 ] [ 2 ] ) ; System. out. p r i n t l n ( "NxM= " + m a t r i x. l e n g t h + " x " + matrix [ 0 ]. length ) ; / / MxN=3x4 / / an exception i s thrown System. out. p r i n t l n ( " m a t r i x [ 4 ] [ 4 ] = " + m a t r i x [ 4 ] [ 4 ] ) ; c Michal Krátký Introduction to Programming (Java) 10/31

11 Branching 1/3 Statement if-else enables to control the run-time of a program. i f ( value > value2 ) r e s u l t = 1 ; else i f ( value1 < value2 ) r e s u l t = 1; else r e s u l t = 0 ; c Michal Krátký Introduction to Programming (Java) 11/31

12 Branching 2/3 We can use a prescript without blocks, however, the program is less readable and the insertion of new statements is more complicated. i f ( value > value2 ) r e s u l t = 1 ; else i f ( value < value2 ) r e s u l t = 1; else r e s u l t = 0 ; // you must insert braces and the new statement i f ( value > value2 ) r e s u l t = 1 ; i ++; else... c Michal Krátký Introduction to Programming (Java) 12/31

13 Branching 3/3 The condition is a boolean expression. Condition operators (&& and ) enables the quick evaluation compare to & and boollean operators. boolean f l a g = false ; i n t k = 0 ; i f ( f l a g && ++ k > 0 ) / / k = 0... c Michal Krátký Introduction to Programming (Java) 13/31

14 Cycles Introduction to Programming (Java) 3/12 Java includes 3 kinds of cycles. are repeated since the control condition is true. for with the fixed number of iterations while with a condition in the cycle s start do-while with a condition in the cycles s end c Michal Krátký Introduction to Programming (Java) 14/31

15 Cycles Introduction to Programming (Java) 3/12 i n t i = 0 ; while (++ i < 2 ) System. out. p r i n t l n ( " i : " + i ) ; / / Output : 1 / / i n t i = 0 ; do System. out. p r i n t l n ( " i : " + i ) ; / / Output : 0, 1 while (++ i < 2 ) ; / / for ( i n t i = 0 ; i < 2 ; i + + ) / / the same as ++ i System. out. p r i n t l n ( " i : " + i ) ; / / Output : 0, 1 c Michal Krátký Introduction to Programming (Java) 15/31

16 Cycles, Appropriate Inscription while ( i < 2 j ) i + + ; / / i n a p p r o p r i a t e i n s c r i p t i o n while ( i < 2 j ) i + + ; / / i n a p p r o p r i a t e ( o f t e n used ) i n s c r i p t i o n while ( i < 2 j ) i + + ; / / a p p r o p r i a t e i n s c r i p t i o n c Michal Krátký Introduction to Programming (Java) 16/31

17 Cycles Introduction to Programming (Java) 3/12 i n t i = 0 ; boolean f l a g = true ; while ( f l a g ) System. out. p r i n t l n ( " i : " + i ) ; / / Output :0,1,2,3 i ++; f l a g = ( i < = 3 ) ; / / i = 0 ; while ( i <= 3) System. out. p r i n t l n ( " i : " + i ) ; / / Output :0,1,2,3 i ++; c Michal Krátký Introduction to Programming (Java) 17/31

18 Cycles,, Example 1/2 f i n a l i n t size = 3 1 ; i n t arraya [ ] = new i n t [ s ize ] ; i n t arrayb [ ] = arraya ; for ( i n t i = 0 ; i < arraya. l e n g t h ; i ++) arraya [ i ] = 1 < < i ; / / the m u l t i p l i c a t i o n by 2 for ( i n t i = 0 ; i < arrayb. l e n g t h ; i ++) System. out. p r i n t l n ( i + " : " + arrayb [ i ] ) ; c Michal Krátký Introduction to Programming (Java) 18/31

19 Cycles,, Example 2/2 Output: 0: 1 1: 2 2: 4 3: 8 4: 16 5: 32 6: 64 7: 128 8: 256 9: : : c Michal Krátký Introduction to Programming (Java) 19/31

20 Cycles,, Example double matrix [ ] [ ] = 1. 0, 0. 0, 0. 0, 0. 0, 1. 0, 0. 0, 0. 0, 0. 0, 1. 0 ; for ( i n t i = 0 ; i < m a t r i x. l e n g t h ; i ++) for ( i n t j = 0 ; j < m a t r i x [ i ]. l e n g t h ; j ++) System. out. p r i n t l n ( " m a t rix [ " + i + " ] [ " + j + " ] = " + m a t r i x [ i ] [ j ] ) ; c Michal Krátký Introduction to Programming (Java) 20/31

21 Control of Cycles 1/2 The control of cycles is possible by break and continue statements. break finishes the cycle without an execution of the rest cycle statements continue finishes the current iteration and continues from the cycle s start c Michal Krátký Introduction to Programming (Java) 21/31

22 Control of Cycles 2/2 for ( i n t i = 0 ; ; i ) i f ( i % 2 = = 0 ) continue ; i f ( ( i + = 2 ) > = 2 0 ) break ; c Michal Krátký Introduction to Programming (Java) 22/31

23 Control of Cycles 2 1/2 In the case of nested break and continue statements, we can use labels. i n t i = 0 ; outer : while ( true ) while ( true ) i ++; i f ( i = = 1 ) break ; i f ( i = = 4 ) break outer ; c Michal Krátký Introduction to Programming (Java) 23/31

24 Control of Cycles 2 2/2 while ( true ) i ++; i f ( i = = 2 ) continue ; i f ( i = = 3 ) continue outer ; c Michal Krátký Introduction to Programming (Java) 24/31

25 switch 1/2 switch is appropriate for a test of an integer expression defining one or more values. switch ( < intexpr >) case intvalue1 :... break ; case intvalue2 : case intvalue3 :... break ;... default :... c Michal Krátký Introduction to Programming (Java) 25/31

26 switch 2/2 i n t state, i ;... switch ( s t a t e ) case 0 : i = 0 ; break ; case 1 : case 2 : i ++; break ; default : i ; c Michal Krátký Introduction to Programming (Java) 26/31

27 Example 3.1 1/3 public class Example0301 public s t a t i c void main ( S t r i n g [ ] args ) S t r i n g s t r = " This i s a s t r i n g " ; char ch = t ; i n t number = 0 ; for ( i n t i = 0 ; i < s t r. l e n g th ( ) ; i ++) i f ( s t r. charat ( i ) = = ch ) number ++; c Michal Krátký Introduction to Programming (Java) 27/31

28 Example 3.1 2/3 switch ( number ) case 0 : System. out. p r i n t ( "No Occurrence " ) ; break ; default : System. out. p r i n t ( " The Number of Occurrences : + number ) ; break ; System. out. p r i n t l n ( ", of the character " + ch + " i n the s t r i n g " + s t r + " " ) ; c Michal Krátký Introduction to Programming (Java) 28/31

29 Example 3.1 3/3 Output: The Number of Occurrences: 1, of the character t in the string This is a string c Michal Krátký Introduction to Programming (Java) 29/31

30 Example 3.2 1/2 The computation of sin for an angle in 0, 2π in the step 0.1. f i n a l double step = 0. 1 ; f i n a l double maxangle = ; f i n a l double maxx = Math. PI 2 ; i n t i = 0 ; for ( double x = 0. 0 ; x <= maxx ; x + = step ) double deg = ( x / Math. PI ) maxangle ; double sinvalue = Math. s i n ( x ) ; System. out. p r i n t l n ((++ i ) + ". Angle : " + x + " ( " + deg + " ), s i n ( ) = " + sinvalue ) ; c Michal Krátký Introduction to Programming (Java) 30/31

31 Example 3.2 2/2 Output: 1. Angle: 0.0 (0.0), sin()= Angle: 0.1 ( ), sin()= Angle: 0.2 ( ), sin()= Angle: 0.3 ( ), sin()= Angle: 0.4 ( ), sin()= Angle: 0.5 ( ), sin()= Angle: 0.6 ( ), sin()= Angle: ( ), sin()= c Michal Krátký Introduction to Programming (Java) 31/31