解きながら学ぶJava入門編

44 // class Negative { System.out.print(""); int n = stdin.nextint(); if (n < 0) System.out.println(""); -10 Ÿ 35 Ÿ 0 n if statement if ( ) if i f ( ) if n < 0 < true false true false boolean literalboolean if Fig.3-1 Fig.3-1

45n 0 true System.out.println(""); n 0 < relational operatortable 3-1 <= >= =< => < = < = Table 3-1 3 x < y x > y x <= y x >= y x y true false x y true false x y true false x y true false if if-then if-then- if Fig.3-2 if if ( ) Fig.3-2 if if ( ) if ( ) if-then if-then- if

46 Java3-1p.59 // class Absolute1 { System.out.print(""); int n = stdin.nextint(); if (n >= 0) System.out.println("" + n + ""); System.out.println("" + (-n) + ""); 62 Ÿ 62-35 Ÿ 35 // class Absolute2 { System.out.print(""); int n = stdin.nextint(); int abs; if (n >= 0) abs = n; abs = -n; System.out.println("" + abs + ""); 0 5-5 5 5 n n 0 n n n -n n 0 Absolute1 if if ( ) if true false Fig.3-3 n 0

47 Fig.3-3 Absolute2 if-then- n abs Absolute1 Absolute2 if-then if-then- 4 4 4 n 0 Fig.3-1 if-then if-then- 3 if (n < 0) System.out.println(""); ; if empty statement Fig.3-4 ; Fig.3-4

48 Java3-3p.59 // class Measure1 { 12 Ÿ 4 Ÿ System.out.print(""); int a = stdin.nextint(); System.out.print(""); int b = stdin.nextint(); if (a % b == 0) System.out.println(""); System.out.println(""); b a a b 0 4 12 12 4 0 5 12 12 5 2 if == ==!= equality operatortable 3-2 true false Table 3-2 x == y x!= y x y true false x y true false!= if if (a % b!= 0) System.out.println(""); System.out.println("");

49! // class Measure2 { System.out.print(""); int a = stdin.nextint(); System.out.print(""); int b = stdin.nextint(); if (!(a % b == 0)) System.out.println(""); System.out.println(""); 12 Ÿ 5 Ÿ 3! logical complement operator false true true false Table 3-3 if a % b 0 a % b == 0 true!(a % b == 0) false a % b 0 a % b == 0 false!(a % b == 0) true Table 3-3!x x false true true false a 1 3 1 <= a <= 3 // && a >= 1 && a <= 3 // a1a3 a b c a == b == c // && a == b && b == c // abbc a == b && a == c // abac

50 JavaList 3-5p.58 // class Sign { System.out.print(""); int n = stdin.nextint(); if (n > 0) System.out.println(""); if (n < 0) System.out.println(""); System.out.println(""); 37 Ÿ 0 Ÿ -35 Ÿ 0 if if ( ) if ( ) if if if Fig.3-5 if if System.out. Fig.3-7 if (n > 0) println(""); if (n < 0) println(""); println(""); Fig.3-5

51 Java3-2p.59 if (n == 0) if if (n > 0) System.out.println(""); if (n < 0) System.out.println(""); if (n == 0) System.out.println(""); n > 0 n < 0 false n 0 n n 0 if 3 if (n == 1) System.out.println(""); if (n == 2) System.out.println(""); if (n == 3) System.out.println(""); n 1 2 3 if if ( ) if ( ) if n 4 5-10 1 2 if (n == 1) System.out.println(""); if (n == 2) System.out.println(""); if (n == 3) System.out.println(""); ; if Sign if if ( )

52 Java3-4p.61 a, b a b a b // class Balance { System.out.print("a"); int a = stdin.nextint(); System.out.print("b"); int b = stdin.nextint(); if (a > b) System.out.println("a"); if (a < b) System.out.println("b"); System.out.println("ab"); a12 Ÿ b3 Ÿ a a5 Ÿ b15 Ÿ b a b if if Fig.3-6 a b a b Fig.3-6

53// class BalanceWrong { System.out.print("a"); int a = stdin.nextint(); System.out.print("b"); int b = stdin.nextint(); int diff = a - b; if (diff > 0) System.out.println("a"); if (diff < 0) System.out.println("b"); System.out.println("ab"); a2147483647 Ÿ b-1 Ÿ b a-2147483648 Ÿ b1 Ÿ a 3 BalanceWrong a b diff 0 a b 2147483647-1 1-2147483648 int -2147483648 +2147483647 2147483647-1 -2147483648 1 int

54 Java3-5p.61 // class GoInto5 { System.out.print(""); int n = stdin.nextint(); if (n > 0) if (n % 5 == 0) System.out.println(""); System.out.println(""); System.out.println(""); 35 Ÿ 36 Ÿ 5 if Fig.3-7 if if if if Fig.3-8 Fig.3-6 4 if (n > 0) if (n % 5 == 0) println(""); println(""); println(""); Fig.3-7

55 Fig.3-8 3 expression abc + 32 abc 32 + abc + 32 xyz = abc + 32 xyz, abc, 32, abc + 32, xyz = abc + 32 4 4 xyz abc + 32 xyz = abc + 32 4 4 assignment expression ; a = c + 32 4 4 Fig.3-9 expression statement ; Fig.3-9

56 Java3-6p.61 10 10 10 // class MultipleOf10 { System.out.print(""); int n = stdin.nextint(); 1250 Ÿ 10 1254 Ÿ 10 if (n > 0) if (n % 10 == 0) System.out.println("10"); System.out.println("10"); System.out.println(""); 10 10 evaluation Fig.3-10 int n 1254 n, 10, n % 10 n 1254 1254, 10, 4 int int 1254 int 10 n % 10 int 4 Fig.3-10

57 Java3-7p.61 3 3 3 1 3 2 // class Modulo3 { System.out.print(""); int n = stdin.nextint(); 1251 Ÿ 3 1253 Ÿ 32 if (n > 0) if (n % 3 == 0) System.out.println("3"); if (n % 3 == 1) System.out.println("31"); System.out.println("32"); System.out.println(""); 3 if if if if if n if (n > 0); System.out.println(""); n (n > 0) ; if if (n > 0) ; // ifn > 0 System.out.println(""); // if if ( )

58 Java3-8p.69 0 59 60 69 70 79 80 100 // && class Grade1 { 68 Ÿ System.out.print(""); int point = stdin.nextint(); if (point >= 0 && point <= 59) System.out.println(""); if (point >= 60 && point <= 69) System.out.println(""); if (point >= 70 && point <= 79) System.out.println(""); if (point >= 80 && point <= 100) System.out.println(""); System.out.println(""); 89 Ÿ 102 Ÿ && Fig.3-11 logical and operator x && y x y true true false x ytable 3-4 true point 0 4 4 59 && x y x && y true true true true false false false true false false false false x y x y true true true true false true false true true false false false Fig.3-11

59 System.out.print(""); int point = stdin.nextint(); if (point < 0 point > 100) System.out.println(""); if (point <= 59) System.out.println(""); if (point <= 69) System.out.println(""); if (point <= 79) System.out.println(""); System.out.println(""); 3 // class Grade2 { Grade2 logical or operator x y x y true true false x y 4 4 4 4 l 4 4 4 point 0 100 true point 0 100 0 59 point 60 100 60 69 Grade2 Grade1 Table 3-4 x && y x y x y true true false x y true true false

60 Java3-9p.71 // if class Max2A { System.out.print("a"); double a = stdin.nextdouble(); System.out.print("b"); double b = stdin.nextdouble(); double max; // if (a > b) max = a; max = b; System.out.println("" + max + ""); a25.7 Ÿ b15.3 Ÿ 25.7 a, b a b max a max b if max Max2B if? : Table 3-5 conditional operator conditional expression Fig.3-12 max a b a b if a > b? a : b a > b? a : b double 25.7 double 3.14 Fig.3-12

61// class Max2B { System.out.print("a"); double a = stdin.nextdouble(); System.out.print("b"); double b = stdin.nextdouble(); double max = a > b? a : b; // System.out.println("" + max + ""); Table 3-5 x? y : z x true y z 3 x true z false y println max System.out.println("" + (a > b? a : b) + ""); ( ) Grade1 point -10 if point >= 0 && point <= 59 point >= 0 false point <= 59 false && false 4 4 4 4 4 Grade2 point < 0 point > 100 point -10 point < 0 true point > 100 true true 4 4 4 4 4 short circuit evaluation && & & & &

62 Java3-10p.71 // if class Diff2A { System.out.print("a"); int a = stdin.nextint(); System.out.print("b"); int b = stdin.nextint(); int diff; if (a >= b) diff = a - b; diff = b - a; System.out.println("" + diff + ""); a12 Ÿ b3 Ÿ 9 a3 Ÿ b12 Ÿ 9 // class Diff2B { System.out.print("a"); int a = stdin.nextint(); System.out.print("b"); int b = stdin.nextint(); int diff = a >= b? a - b : b - a; System.out.println("" + diff + ""); 0 Diff2A if Diff2B println diff System.out.println("" + (a >= b? a - b : b - a) + "");

63 Java3-11p.71 10 10 11 // 10 class Diff2digits1 { System.out.print(""); int a = stdin.nextint(); System.out.print(""); int b = stdin.nextint(); int diff = a >= b? a - b : b - a; if (diff <= 10) System.out.println("10"); System.out.println("11"); 12 Ÿ 3 Ÿ 10 35 Ÿ 23 Ÿ 11 3 // 10 class Diff2digits2 { System.out.print(""); int a = stdin.nextint(); System.out.print(""); int b = stdin.nextint(); int diff = a >= b? a - b : b - a; System.out.println("" + (diff <= 10? "10" : "11") + ""); a b Diff2B Diff2digits1 if Diff2digits2 Diff2digits2 "" ""

64 Java3-12p.73 // class Min3 { System.out.print("a"); int a = stdin.nextint(); System.out.print("b"); int b = stdin.nextint(); System.out.print("c"); int c = stdin.nextint(); int min = a; if (b < min) min = b; if (c < min) min = c; System.out.println("" + min + ""); a3 Ÿ b1 Ÿ c2 Ÿ 1 a, b, c min a b min min b c min min c algorithm Fig.3-13 Fig.3-13

65 a, b, c 3, 1, 2 Fig.3-14 min a, b, c 1, 2, 3 3, 2, 1 5, 5, 5 3, 1, 3 int min = a; if (b < min) min = b; a = 3 b = 1 c = 2 min 3 1 a = 1 b = 2 c = 3 min 1 1 a = 3 b = 2 c = 1 min 3 2 a = 5 b = 5 c = 5 min 5 5 a = 3 b = 1 c = 3 min 3 1 3 if (c < min) min = c; 1 1 1 5 1 Fig.3-14

66 Java3-13p.73 1, 2, 3 2 3, 2, 3 3 4, 4, 4 4 // class Med3 { System.out.print("a"); int a = stdin.nextint(); System.out.print("b"); int b = stdin.nextint(); System.out.print("c"); int c = stdin.nextint(); int med; if (a >= b) if (b >= c) med = b; if (a <= c) med = a; med = c; if (a > c) med = a; if (b > c) med = c; med = b; a152 Ÿ b324 Ÿ c75 Ÿ 152 System.out.println("" + med + ""); Fig.3-15 a, b, c median Med3 med,,, Fig.3-15 if ((b >= a && c <= a) (b <= a && c >= a)) med = a; if ((a > b && c < b) (a < b && c > b)) med = b; med = c;

67 3 Fig.3-15 Fig.3-16 Fig.3-16

68 Java3-14p.77 // class MinMaxEq { System.out.print("a"); int a = stdin.nextint(); System.out.print("b"); int b = stdin.nextint(); if (a == b) System.out.println(""); { a12 Ÿ b3 Ÿ 3 12 int min, max; // if (a < b) { // ab min = a; max = b; a17 Ÿ { b17 Ÿ min = b; max = a; System.out.println("" + min + ""); System.out.println("" + max + ""); a == b Fig.3-17 if (a == b) System.out.println(""); { int min, max; if (a < b) { min = a; max = b; { min = b; max = a; System.out.println("" + min + ""); System.out.println("" + max + ""); if () { if Fig.3-17

69{ if { block Fig.3-18 { Fig.3-18 3 if if ( ) if ( ) 4 4 4 4 4 4 4 4 4 4 4 4 if if min max if if a b { min = a; max = b; { min = b; max = a; if { if if if if (a < b) min = a; max = b; min = b; max = a; if ( ) ;

70 Java3-15p.77 // class Sort2Descending { System.out.print("a"); int a = stdin.nextint(); System.out.print("b"); int b = stdin.nextint(); if (a < b) { // ab int t = a; a = b; b = t; // System.out.println("ab"); System.out.println("a" + a + ""); System.out.println("b" + b + ""); a13 Ÿ b57 Ÿ ab a57 b13 a, b a b sort a b a b a b t a t b a t a b a b a 13 b 57 Fig.3-19 a 57 b 13

71 a a 13 b t b 57 Fig.3-19 t - 13 57 13 57 57 13 t = a; a = b; b = t; if if 1 2 57 13 13 if (a == 1) if (b == 1) 1 2 if if if if (a == 1) if (b == 1) 3 1 a 1 b 1 1 a 1 b 1 2 a 1 2 a 1 b 1 if a 1 if (a == 1) if (b == 1) 1 2 if (a == 1) { if (b == 1) 1 2

72 Java3-16p.77 // class Sort3 { System.out.print("a"); int a = stdin.nextint(); System.out.print("b"); int b = stdin.nextint(); System.out.print("c"); int c = stdin.nextint(); if (a > b) { // abab int t = a; a = b; b = t; if (b > c) { // bcbc int t = b; b = c; c = t; if (a > b) { // abab int t = a; a = b; b = t; System.out.println("abc"); System.out.println("a" + a + ""); System.out.println("b" + b + ""); System.out.println("c" + c + ""); a53 Ÿ b35 Ÿ c42 Ÿ abc a35 b42 c53 a, b, c if Fig.3-20 a, b, c 5, 3, 2 if t t a b a b if b c b c c if c c a, b b if

73if (a > b) ab if (b > c) bc if (a > b) ab Fig.3-20 a b c 5 3 2 3 5 2 3 2 5 2 3 5 a b b 5 3 2 a b c c b a Fig.3-21 a, b, c 5, 3, 4 a > b 3 if (a > b) ab if (b > c) bc if (a > b) ab a b c 5 3 4 3 5 4 3 4 5 3 4 5 5 3 4 a b c Fig.3-21

74 Java3-17p.83 0, 1, 2 0 "" 1 "" 2 "" // import java.util.random; class FingerFlashing { Random rand = new Random(); System.out.print(""); int hand = rand.nextint(3); // 02 switch (hand) { case 0: System.out.println(""); break; case 1: System.out.println(""); break; case 2: System.out.println(""); break; 0 ""1 ""2 "" switch statement switch switch ( ) switch hand 1 case 1: case 1 label hand 1 Fig.3-22 System.out.println(""); break statement break; switch

75 switch ( hand ) { case 0: System.out.println(""); break; case 1: System.out.println(""); break; case 2: System.out.println(""); break; Fig.3-22 break switch hand 1 "" "" hand 0 "" 2 "" break switch switch hand 0, 1, 2 switch 3 case 2 "" break break switch break 3 switch switch (hand) { case 0: System.out.println(""); break; case 1: System.out.println(""); break; case 2: System.out.println(""); break; case 3: System.out.println(""); break; switch case 2: break case 2: break break break

76 Java3-18p.83 1 12 // class Season { System.out.print(""); int month = stdin.nextint(); 6 Ÿ 11 Ÿ switch (month) { case 3 : case 4 : case 5 : System.out.println(""); break; case 6 : case 7 : case 8 : System.out.println(""); break; case 9 : case 10 : case 11 : System.out.println(""); break; case 12 : case 1 : case 2 : System.out.println(""); break; default : System.out.println(""); break; 13 Ÿ switch default: case default break month 3 4 5 switch switch if switch selection statement Fig.3-23 switch ( ) char, byte, short, int, Character, Byte, Short, Integer,

77{ case : default Fig.3-23 break Fig.3-24 break 3 switch switch ( ) break break ; Fig.3-24 if switch switch Fig.3-25 if if a 4 if b 4 c 80 a 1, 2, 3 b 4 if if (a == 4) if (a == 4) switch if (a == 1) c = 10; if (a == 2) c = 20; if (a == 3) c = 50; if (b == 4) c = 80; // ifswitch switch (a) { case 1 : c = 10; break; case 2 : c = 20; break; case 3 : c = 50; break; default : if (b == 4) c = 80; break; Fig.3-25

78 if keyword Table 3-6 Table 3-6 abstract assert boolean break byte case catch char class const continue default do double enum extends final finally float for goto if implements import instanceof int interface long native new package private protected public return short static strictfp super switch syncronized this throw throws transient try void volatile while const goto truefalsenull separator Table 3-7 Table 3-7 [ ] ( ) {, :. identifier $ _ $ _ true false null $

79 v v1 va $x $1 _1 If X1000 1 9801 1$!! if #911 -x {x #if 0-1-2 operator Table 3-8 precedence * / + - a + b * c (a + b) * c a + (b * c) + * + ( ) // *+( ) System.out.println("ab" + a * b + ""); //?:+( ) System.out.println("" + (a > b? a : b) + ""); 3 + ( ) ( ) associativity a b c (a b) c a (b c) - 5-3 - 1 (5-3) - 1 // - 5 - (3-1)

80 Table 3-8 [ ] x[y] ( ) x(arg opt ). x.y ++ x++ -- x-- ++ ++x -- --x + +x + - -x -!!x ~ ~x new new new ( ) ( ) * x * y / x / y % x % y + x + y - x - y << x << y >> x >> y >>> x >>> y < x < y > x > y <= x <= y >= x >= y instanceof x instanceof y instanceof == x == y!= x!= y & x & y ^ x ^ y x y && x && y

81 /= x /= y %= x %= y += x += y -= x -= y <<= x <<= y >>= x >>= y >>>= x >>>= y 3 x y? : x? y : z = x = y *= x *= y &= x &= y ^= x ^= y = x = y x int x = 2 x int 2 a b int Fig.3-26 a = b = 1 a = (b = 1) // = b = 1 b 1 b = 1 b int 1 a a b 1 int 1 int 1 Fig.3-26 a = b = 1

82 (1) (1) (2) (3) { (4) a + b * c * (5) + (5) (6) <, >, <=, >= (7) ==,!= (8) &&, (9)! (10)? : (11) (12) if (13) (14) (15) (16) (17) int a = 1, b = 3, c = 5; System.out.println("a < b : " + (a < b)); System.out.println("a <= b : " + (a <= b)); System.out.println("b > c : " + (b > c)); System.out.println("b >= c : " + (b >= c)); System.out.println("a == b : " + (a == b)); System.out.println("a!= b : " + (a!= b)); System.out.println("a - b - c : " + (a - b - c)); System.out.println("c - b - a : " + (c - b - a)); System.out.println("a = b = c : " + (a = b = c)); System.out.println("c = b = a : " + (c = b = a)); a < b : a <= b : b > c : b >= c : a == b : a!= b : a - b - c : c - b - a : a = b = c : c = b = a : (18)

83 x y x && y false false (19) false true (20) true false (21) true true (22) x y x y false false (23) false true (24) true false (25) true true (26) c 0 50 250 c 0 (27) (c (28) 10 == 0) System.out.println("c0"); 3 x 0 (29) (x == 0) System.out.println(""); (30) System.out.println(""); a System.out.println("a" + (31) ); a b System.out.println("ab" + (32) ); System.out.println("ab" + (33) ); w 0 1 2 (34) (w) { (35) 0: System.out.println(""); (36) ; (35) 1: System.out.println(""); (36) ; (35) 2: System.out.println(""); (36) ;

84 (37) (38) + (39) = (40) m 3, 4, 5 if ( (41) (42) (43) ) System.out.println(""); System.out.println(""); if ( (44) && (45) ) System.out.println(""); System.out.println(""); if ( (46) ( (47) (48) )) System.out.println(""); System.out.println(""); m3 if ( (49) ) System.out.println(""); (50) System.out.println(""); (51) System.out.println(""); switch ( (52) ) { case (53) System.out.println(""); break; case (54) System.out.println(""); break; case (55) System.out.println(""); break; a b if ( (56) ) System.out.println("ab"); System.out.println("ab");

85 switch int n 1, 2, 3 (60) (61) (62) int n 0, 1 (63) (64) switch (n) { case 1: System.out.print("A"); case 2: System.out.print("B"); break; default: System.out.print("C"); if (n == 0); System.out.println("A"); 3 a b a b if ( (57) ) { int t = a; a = (58) ; b = (59) ; a b a b if (a * (65) < (66) ) System.out.println("ab"); a, b, c if ( (67) && (68) ) System.out.print(""); a b import (69).util.Scanner; (70) Even { public (71) void main( (72) args) { System.out.print(""); int a = (73).nextInt(); System.out.print(""); int b = (73).nextInt(); int c = 0; if ( (74) ) c = c + 1; if ( (75) ) c = c + 1; if ( (76) == 0) System.out.println(""); if ( (77) ) System.out.println(""); if ( (78) ) System.out.println("");