复习CS61B project1之前的题目
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lab 1 考点：
substring/concat/equals/equalsIgnoreCase/indexOf
all index from 0 not 1.
homework 1 考点：
opencommerical是老师上课讲过的例子，现学现卖／怎样读取网页检查元素／readline()会自动向下一个进行读取
1 class OpenCommerical { 2 3 /** Prompts the user for the name X of a company (a single string), opens 4 * the Web site corresponding to www.X.com, and prints the first five lines 5 * of the Web page in reverse order. 6 * @param arg is not used. 7 * @exception Exception thrown if there are any problems parsing the 8 * user‘s input or opening the connection. 9 */ 10 public static void main(String[] arg) throws Exception { 11 12 BufferedReader keyboard; 13 String inputLine; 14 15 keyboard = new BufferedReader(new InputStreamReader(System.in)); 16 17 System.out.print("Please enter the name of a company (without spaces): "); 18 System.out.flush(); /* Make sure the line is printed immediately. */ 19 inputLine = keyboard.readLine(); 20 21 /* Replace this comment with your solution. */ 22 URL u = new URL("http://www."+inputLine+".com/"); 23 InputStream ins = u.openStream(); 24 InputStreamReader isr = new InputStreamReader(ins); 25 String[] FiveLines = new String[5]; 26 BufferedReader Baidu = new BufferedReader(isr); 27 for(int i=0; i<5 ;i++){ 28 FiveLines[i] = Baidu.readLine(); 29 } 30 for(int j=4;j>=0;j--){ 31 System.out.println(FiveLines[j]); 32 } 33 } 34 }
nuke2 substring运用
lab2 考点
gcd辗转相除
static private int gcd (int x, int y) { //辗转相除法 /* Replace the following line with your solution. */ if(y==0) return x; else return gcd(y,x%y); }
构造函数
System.out.println("..." + d1);//这里d1会自动调用toString(); 可以不用写出来。
1 class Fraction { 2 3 /* private fields within a Fraction. */ 4 static private int numberOfFractions = 0; 5 6 private int numerator; 7 private int denominator; 8 9 /** Constructs a Fraction n/d. 10 * @param n is the numerator. Must be nonnegative. 11 * @param d is the denominator. Must be positive. 12 */ 13 public Fraction(int n, int d) { 14 if (n < 0) { 15 System.out.println("Fatal error: Negative numerator."); 16 System.exit(0); 17 } 18 if (d < 1) { 19 System.out.println("Fatal error: Non-positive denominator."); 20 System.exit(0); 21 } 22 numberOfFractions++; 23 numerator = n; 24 denominator = d; 25 } 26 27 /** Constructs a Fraction n/1. 28 * @param n is the numerator. Must be nonnegative. 29 */ 30 public Fraction(int n) { 31 this(n, 1); //call the two-parameters constructor 32 } 33 34 /** Constructs a Fraction 0/1. 35 */ 36 public Fraction() { 37 this(0,1); // call the two-parameters constructor 38 } 39 40 /** Copies the Fraction "original". 41 */ 42 public Fraction(Fraction original) { 43 this(original.numerator,original.denominator); 44 } 45 46 /** Converts this Fraction to a string format: "numerator/denominator." 47 * Fractions should be printed in reduced form (part of your assignment is 48 * to make this true). 49 * @return a String representation of this Fraction. 50 */ 51 public String toString() { 52 int thisGcd = gcd(numerator, denominator); 53 54 return (numerator / thisGcd + "/" + denominator / thisGcd); 55 } 56 57 /** Return the sum of two fractions. 58 * @param f2 is the Fraction to be added. 59 * @return the result of adding f2 to this Fraction. 60 */ 61 public Fraction add(Fraction f2) { 62 Fraction r = new Fraction((numerator * f2.denominator) + 63 (f2.numerator * denominator), 64 denominator * f2.denominator); 65 return r; 66 } 67 68 /** Replaces this Fraction‘s numerator with a new value. 69 * @param numerator is the new numerator. Must be nonnegative. 70 */ 71 public void changeNumerator(int numerator) { // DO NOT CHANGE THIS SIGNATURE! 72 // Fix the bug that prevents this method from working correctly. 73 if (numerator < 0) { 74 System.out.println("Fatal error: Negative numerator."); 75 System.exit(0); 76 } 77 this.numerator = numerator; 78 79 } 80 81 /** Returns the number of Fraction objects in existence. 82 * @return the number of Fraction objects in existence. 83 */ 84 public int fracs() { // DO NOT CHANGE THIS SIGNATURE! 85 // Fix the bug that prevents this method from working correctly. 86 return numberOfFractions; 87 } 88 89 /** Computes the greatest common divisor (gcd) of the two inputs. 90 * @param x must be nonnegative 91 * @param y must be nonnegative 92 * @return the gcd of x and y 93 */ 94 static private int gcd (int x, int y) { //辗转相除法 95 /* Replace the following line with your solution. */ 96 if(y==0) 97 return x; 98 else 99 return gcd(y,x%y); 100 } 101 102 /** Put the Fraction class through some tests. 103 * @param argv is not used. 104 */ 105 public static void main(String[] argv) { 106 107 /* Test all four contructors and toString. */ 108 Fraction f0 = new Fraction(0,1); 109 Fraction f1 = new Fraction(3); 110 Fraction f2 = new Fraction(12, 20); 111 Fraction f3 = new Fraction(f2); 112 113 System.out.println("\nTesting constructors and toString():"); 114 System.out.println("The fraction f0 is " + f0.toString()); 115 System.out.println("The fraction f1 is " + f1); // toString is implicit. 116 System.out.println("The fraction f2 is " + f2); 117 System.out.println("The fraction f3 is " + f3 + ", which should equal f2"); 118 119 /* Test the add method. */ 120 System.out.println("\nTesting add:"); 121 122 123 124 Fraction sumOfTwo = f1.add(f2); // Sum of f1 and f2. 125 Fraction sumOfThree = f0.add(f1).add(f2); // Sum of f0, f1, and f2. 126 127 System.out.println("The sum of " + f1 + " and " + f2 + " is " + sumOfTwo); 128 System.out.println("The sum of " + f0 + ", " + f1 + " and " + f2 + " is " + 129 sumOfThree); 130 131 132 /* Test the methods used in Part III. */ 133 System.out.println("\nTesting changeNumerator and fracs:"); 134 135 f3.changeNumerator(7); 136 System.out.println("Now f3 is " + f3 + ", which should be 7/20"); 137 System.out.println("The total number of Fraction objects is " + 138 f3.fracs()); 139 140 /* Test gcd function (static method). */ 141 System.out.println("\nTesting gcd:"); 142 System.out.println("The gcd of 2 and 10 is: " + gcd(2, 10)); 143 System.out.println("The gcd of 15 and 5 is: " + gcd(15, 5)); 144 System.out.println("The gcd of 24 and 18 is: " + gcd(24, 18)); 145 System.out.println("The gcd of 10 and 10 is: " + gcd(10, 10)); 146 System.out.println("The gcd of 21 and 400 is: " + gcd(21, 400)); 147 } 148 }
homework2考点
闰年判断
public static boolean isLeapYear(int year) { if((year%4==0&&year%100!=0)||(year%400==0)){ return true; }else return false; // replace this line with your solution }
正则表达+split分割字符串+Integer.parseInt()方法将String转化为int
public Date(String s) { if(s.matches("\\d{1,2}\\/\\d{1,2}\\/\\d{1,4}")){ String[] d=s.split("/"); month=Integer.parseInt(d[0]); day=Integer.parseInt(d[1]); year=Integer.parseInt(d[2]); }else System.exit(0); }
string int 相互转换知识补充
http://blog.csdn.net/memray/article/details/7312817/ 转自MemRay博客
String ==》int
1). int i = Integer.parseInt([String]); 或
i = Integer.parseInt([String],[int radix]);
2). int i = Integer.valueOf(my_str).intValue();
int ==》String
1.) String s = String.valueOf(i);
2.) String s = Integer.toString(i);
3.) String s = "" + i;
注: Double, Float, Long 转成字串的方法大同小异.
未完......................
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