Java_第七章程序清单

程序清单7-1（找到大于平均值的那些项的和）

import java.util.*;

public class AnalyzeNumbers {

public static void main(String[] args) {

// TODO Auto-generated method stub

java.util.Scanner input = new java.util.Scanner(System.in);

System.out.print("Enter the number of times: ");

int n = input.nextInt();

double [] numbers = new double[n];

double sum = 0;

System.out.print("Enter the numbers: ");

for(int i = 0; i < n; i++) {

numbers[i] = input.nextDouble();

sum += numbers[i];

}

double average = sum / n;

int count = 0;

for (int i = 0; i < n; i++)

if (numbers[i] > average)

count++;

System.out.println("Average is " + average);

System.out.println("Number of elements above the average is "+ count);

}

}

程序清单7-2（从一副牌中随机选出四张牌）

public class DeckOfCards {

public static void main(String[] args) {

// TODO Auto-generated method stub

int[] deck = new int[52];

String[] suits = {"Spades", "Hearts", "Diamonds", "Clubs"};//黑桃红桃方块梅花

String[] ranks = {"Ace", "2", "3", "4", "5", "6", "7", "8", "9", "10", "Jack", "Queen", "King"};

for(int i = 0; i < deck.length; i++)

deck[i] = i;

for(int i = 0; i < deck.length; i++) {

int index = (int)(Math.random() * deck.length);

int temp = deck[i];

deck[i] = deck[index];

deck[index] = temp;

}//随机生成牌

for(int i = 0; i < 3; i++) {

String suit = suits[deck[i] / 13];

String rank = ranks[deck[i] % 13];

System.out.println("Card number " + deck[i] + ": " + rank + " of " + suit);

}

}

程序清单7-3（两个交换数组中的元素）

//对于基本数据类型，传递的是实参的值

//对于数组类型的参数，参数值是数组的引用，给方法传递就是这个引用

public class TestPassArray {

public static void main(String[] args) {

// TODO Auto-generated method stub

int[] a = {1, 2};

System.out.println("Befor invoking swap");

System.out.println("array is {" + a[0] + ", " + a[1] + "}");

System.out.println("After invoking swap");

swap(a[0],a[1]);

System.out.println("array is {" + a[0] + ", " + a[1] + "}");

System.out.println("Befor invoking swapFirstTowArray");

System.out.println("array is {" + a[0] + ", " + a[1] + "}");

swapFirstTowArray(a);

System.out.println("After invoking swapFirstTowArray");

System.out.println("array is {" + a[0] + ", " + a[1] + "}");

}

public static void swap(int n1, int n2) {

int temp = n1;

n1 = n2;

n2 = temp;

}

public static void swapFirstTowArray(int[] array) {

int temp = array[0];

array[0] = array[1];

array[1] = temp;

}

}

程序清单7-4（丛集一个字母出现的次数）

public class CountLetterInArray {

public static void main(String[] args) {

// TODO Auto-generated method stub

char[] chars = createArray();//生成存100个放随机小写字母

System.out.println("The lowercase letters are: ");

displayArray(chars);

int[] counts = countLetters(chars);

System.out.println();

System.out.println("The pccurrences of cech letter are:");

displayCounts(counts);

}

public static char[] createArray() {

char[] chars = new char[100];

for(int i = 0; i < chars.length; i++)

chars[i] = RandomCharacter.getRandomLowerCaseLetter();

return chars;

}

public static void displayArray(char[] chars) {

for(int i = 0; i < chars.length; i++) {

if((i+1) % 20 == 0)

System.out.println(chars[i]);

else

System.out.println(chars[i] + " ");

}

}

public static int[] countLetters(char[] chars) {//计数

int[] counts = new int[26];

for (int i = 0; i < chars.length; i++)

counts[chars[i] - 'a']++;

return counts;

}

public static void displayCounts(int[] counts) {

for(int i = 0; i < counts.length; i++) {

if((i + 1) % 10 == 0)

System.out.println(counts[i] + " " + (char)(i + 'a'));

else

System.out.print(counts[i] + " " +(char)(i + 'a') + " ");

}

}

}

程序7-5（可变参数列表，求最大值）

public class VarArgsDemo {

public static void main(String[] args) {

// TODO Auto-generated method stub

printMax(34, 3, 3, 2, 56, 56.5);

printMax(new double[]{1, 2, 3});

}

public static void printMax(double...numbers) {

if(numbers.length == 0) {

System.out.println("No argument passed");

return;

}

double result = numbers[0];

for(int i = 1; i < numbers.length; i++)

if(numbers[i] > result)

result = numbers[i];

System.out.println("The max value is " + result);

}

}