2022年chapter7

1、第七章幾個基本的java 類7.1 math 類1、常用的數學方法成員變量static double ethe double value that is closer than any other to e, the base of the natural logarithms. static double pi the double value that is closer than any other to pi, the ratio of the circumference of a circle to its diameter. 成員方法static double abs(double

2、 a) returns the absolute value of a double value. static float abs(float a) returns the absolute value of a float value. static int abs(int a) returns the absolute value of an int value. static long abs(long a) returns the absolute value of a long value. static double ceil(double a) returns the smal

3、lest (closest to negative infinity) double value that is not less than the argument and is equal to a mathematical integer. static double cos(double a) returns the trigonometric cosine of an angle. static double exp(double a) returns the exponential number e (i.e., 2.718.) raised to the power of a d

4、ouble value. static double floor(double a) returns the largest (closest to positive infinity) double value that is not greater than the argument and is equal to a mathematical integer. static double log(double a) returns the natural logarithm (base e) of a double value. static double max(double a, d

5、ouble b) returns the greater of two double values. static float max(float a, float b) returns the greater of two float values. static int max(int a, int b) returns the greater of two int values. 精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 1 頁，共 11 頁 - - - - - - - - -精品學習資料 可選擇p d f - - - - - - - -

6、 - - - - - - 第 1 頁，共 11 頁 - - - - - - - - -static long max(long a, long b) returns the greater of two long values. static double min(double a, double b) returns the smaller of two double values. static float min(float a, float b) returns the smaller of two float values. static int min(int a, int b)

7、returns the smaller of two int values. static long min(long a, long b) returns the smaller of two long values. static double pow(double a, double b) returns of value of the first argument raised to the power of the second argument. static double random() returns a double value with a positive sign,

8、greater than or equal to 0.0 and less than 1.0. static long round(double a) returns the closest long to the argument. static int round(float a) returns the closest int to the argument. static double sin(double a) returns the trigonometric sine of an angle. static double sqrt(double a) returns the co

9、rrectly rounded positive square root of a double value. static double tan(double a) returns the trigonometric tangent of an angle. static double atan(double a) returns the arc tangent of an angle, in the range of - pi/2 through pi/2.static double toradians(double angdeg) converts an angle measured i

10、n degrees to the equivalent angle measured in radians.2、程序演示精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 2 頁，共 11 頁 - - - - - - - - -精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 2 頁，共 11 頁 - - - - - - - - -運行結果為：3、產生 9個 100 以內的隨機數精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 3 頁，共 11 頁 - - - - - -

11、 - - -精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 3 頁，共 11 頁 - - - - - - - - -public class mathdemo2 public static void main(string args) int r; for (int i=1;i10;i+) r = (int)( 100*math.random() ); system.out.println( random()= + r ); 7.2 數組1、數組基礎在 java 里，數組就是對象，數組類型是引用類型，數組變量實際上是對數組的引用。java數組是動態(tài)分

12、配的，并在分配過程中記錄數組的長度。1）建立數組第一步：聲明數組類型 數組名；如： int a ；第二步：分配數組空間數組名 new 數組類型 n 其中 n 是正整數，表示數組大小如： a = new int5 ；第三步：給數組元素賦值a0 = 0; a1 = 1; a2 = 1; a3 = 1; a4 = 1; 或者三步合而為一，在定義數組時直接初始化他的值：如： int a= 0 , 1 , 2 , 3 , 4 ; 2）例程public class arrayforms1 public static void main(string args) /int a=3,7,9; int a=ne

13、w int3; for(int i = 0; i 3; i+) system.out.print(ai+ ); system.out.println(); a0=3; a1=7; 精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 4 頁，共 11 頁 - - - - - - - - -精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 4 頁，共 11 頁 - - - - - - - - -a2=9; for(int i = 0; i 3; i+) system.out.print(ai+ ); system.o

14、ut.println(); boolean b=new boolean3; for(int i = 0; i 3; i+) system.out.print(bi+ ); b0=true; b2=true; system.out.println(); for(int i = 0; i 3; i+) system.out.print(bi+ ); 運行結果：0 0 0 3 7 9 false false false true true true 從中我們可以看到：int a=3,7,9; 等價于int a=new int3; a0=3; a1=7; a2=9; 2、數組長度數組是對象，java給

15、了他一個成員變量length ，表示數組的長度。int a=3,7,9; int len = a.length; / len=3 舉例：public class array2 static void m(int a) for(int i = 0; i a.length; i+) system.out.print(ai+ ); 精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 5 頁，共 11 頁 - - - - - - - - -精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 5 頁，共 11 頁 - - -

16、 - - - - - -system.out.println(); public static void main(string args) int a1=3,7,9; int a2=1,3,6,0; m(a1); m(a2); 3、對象數組數組元素是對象，這樣的數組稱為對象數組。mankind people = new mankind() , new mankind() , new mankind() ; 等價于mankind people = new mankind 3; people0 = new mankind(); people1 = new mankind(); people2 =

17、 new mankind(); 程序演示：運行結果： 0 0 0 1 2 3 精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 6 頁，共 11 頁 - - - - - - - - -精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 6 頁，共 11 頁 - - - - - - - - -4、多維數組1）建立一個二維數組int a = 1,2,3,4; 二維數組a 是由兩個一維數組a0、a1構成的。int b = 1,2,3,4,5,6,7,8; 二維數組中的一維數組長度可以不同。注意：int c = 1,2,

18、3,4,5,6,7,8 ; 非法2）二維數組的長度int a = 1,2,3,4; int b = 1,2,3,4,5,6,7,8; a.length 的值為 2 b.length 的值為 4 a0.length 的值為 2 b2.length 的值為 3 程序演示：public class array5 public static void main(string args) int a = 1,2,3,4,5,6; system.out.println(a.length:+a.length); system.out.println(a0.length:+a0.length); for(in

19、t i = 0; i a.length; i+) for(int j = 0; j ai.length; j+) system.out.println(int array+i+j+=+ aij); 參見教材 p187 頁程序 array6.java 5、與數組有關的運行錯誤1） public class array7 public static void main(string args) int t=1,2,3,4,5,6; system.out.print(t12); 2） public class array8 public static void main(string args) /

20、inta=new int0;/compile and run ok /intb=new int3.1;/compile error 精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 7 頁，共 11 頁 - - - - - - - - -精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 7 頁，共 11 頁 - - - - - - - - -intc=new int-3;/compile ok but run error 7.3 string 類string 類表示字符串，而字符串是雙引號中的內容。1、字符串的

21、聲明和賦初值string s = “ it is a string ” ; 等價于string s = new string(); s = “ it is a string ” ; 2、string 類中的方法成員方法 char charat (int index) returns the character at the specified index. int compareto(string anotherstring) compares two strings lexicographically. int comparetoignorecase(string str) compares

22、 two strings lexicographically, ignoring case considerations. string concat(string str) concatenates the specified string to the end of this string. boolean equals(object anobject) compares this string to the specified object. boolean equalsignorecase(string anotherstring) compares this string to an

23、other string, ignoring case considerations. int indexof (string str) returns the index within this string of the first occurrence of the specified substring. int indexof (string str, int fromindex) returns the index within this string of the first occurrence of the specified substring, starting at t

24、he specified index. int length() returns the length of this string. string replace(char oldchar, char newchar) returns a new string resulting from replacing all occurrences of oldchar in this string with newchar. boolean startswith (string prefix) tests if this string starts with the specified prefi

25、x. boolean startswith (string prefix, int toffset) tests if this string starts with the specified prefix beginning a specified index. 精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 8 頁，共 11 頁 - - - - - - - - -精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 8 頁，共 11 頁 - - - - - - - - -string substring(i

26、nt beginindex) returns a new string that is a substring of this string. string substring(int beginindex, int endindex) returns a new string that is a substring of this string. char tochararray () converts this string to a new character array. string tolowercase() converts all of the characters in th

27、is string to lower case using the rules of the default locale, which is returned by locale.getdefault. string tostring() this object (which is already a string!) is itself returned. string touppercase() converts all of the characters in this string to upper case using the rules of the default locale

28、, which is returned by locale.getdefault. string trim () removes white space from both ends of this string. static string valueof(object obj) returns the string representation of the object argument. 參見教材第192 頁程序 stringmethod1.java 3、比較字符串的方法演示精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 9 頁，共 11 頁 - - - - - - - - -精品學習資料 可選擇p d f - - - - - - - - - - - - - - 第 9 頁，共 11 頁 - - - - - - - - -7.4 main 方法public c