第7章一维数组（程序清单）_analyzenumber.java-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_43783669/article/details/127037490

7-1 AnalyzeNumbers.java from page 219 （示例学习）

用户输入个数，找到大于平均值的项的数目

class demo {
    public static void main(String[] args) {

        //0 create a Scanner
        java.util.Scanner input = new java.util.Scanner(System.in);

        //1 decide the number of items
        System.out.print("enter the number of items:");
        int n = input.nextInt();
        double[] numbers = new double[n];

        //2 initialize sum
        double sum = 0;

        //3 deciede the numbers in the array
        System.out.print("enter the numbers:");
        for (int i = 0; i < n ; i++) {
            numbers[i] = input.nextDouble();
            //4 sum
            sum += numbers[i];
        }

        //5 count the average
        double average = sum / n;

        //6 decide whether the number is larger than average
        int count = 0;
        for (int i = 0 ; i < n ; i++) {
            if (numbers[i] > average) {
                count++;
            }
        }
        //7 display
        System.out.println("average is " + average);
        System.out.println("number of elements above the average is " + count);
    }
}

7-2 DeckOfCards.java from page 221（示例学习）

打乱一副牌的顺序，随机选择4张

class demo {
    public static void main(String[] args) {
        //0 initialize the array
        int[] deck = new int[52];
        String[] suits = {"Spades", "Hearts" ,"Diamonds" , "Clubs"};
        String[] ranks = {"Ace", "2" , "3","5","6","7","8","9","10","Jack","Queen","King"};

        //1 initialize the cards
        for (int i = 0; i < deck.length; i++) {
            deck[i] = i;
        }
        //2 shuffle the cards
        for (int i = 0; i < deck.length; i++) {
            //generate an index randomly
            int index = (int)(Math.random() * deck.length);
            int temp = deck[i];
            deck[i] = deck[index];
            deck[index] = temp;
        }
        //3 display the 1st 4 cards
        for (int i = 0; i < 4 ;i++) {
            String suit = suits[deck[i] / 13];
            String rank = ranks[deck[i] % 13];
            System.out.println("card number " + deck[i] + ":"
            +rank+" of " + suit);
        }
    }
}

7-3 TestPassArray.java from page 225

比较传递基本数据类型值与传递数组引用变量给方法的不同

public class demo {
    public static void main(String[] args) {
        int[] a = {1, 2};

        // swap elements using the swap method
        System.out.println("before invoking swap");
        System.out.println("array is {" + a[0] + " , " + a[1] + "}");
        swap(a[0], a[1]);
        System.out.println("after invoking swap");
        System.out.println("array is {" + a[0] + " , " + a[1] + "}");

        //swap elements using the swapFirstTwoInArray method
        System.out.println("before invoking swapFirstTwoInArray method");
        System.out.println("array is {" + a[0] + " , " + a[1] + "}");
        swapFirstTwoInArray(a);
        System.out.println("after invoking swap");
        System.out.println("array is {" + a[0] + " , " + a[1] + "}");
    }

        /** swap 2 variables */
        public static void swap(int n1,int n2) {
            int temp = n1;
            n1 = n2;
            n2 = temp; 
        }

        /** swap the 1st 2 elements in the array*/
        public static void swapFirstTwoInArray(int[] array) {
            int temp = array[0];
            array[0] = array[1];
            array[1] = temp;
        }
}

7-4 CountLetterArray.java from page 227（示例学习）

随机生成100个小写字母，并将其放入一个字符数组中，对数组中每个字母出现的次数进行计数

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        //0 declare and create an array
        char[] chars = createArray();
        //1 display the array
        System.out.println("the lowercase letters are:");
        displayArray(chars);
        //2 count the occurrences of each letter
        int[] counts = countLetters(chars);
        //3 display counts
        System.out.println();
        System.out.println("the occurrences of each letter are:");
        displayCounts(counts);
    }
    //** create an array of characters */
    public static char[] createArray() {
        //declare an array of characters and create it
        char[] chars = new char[100];

        //create lowercase letters randomly and assign
        //them to the array
        for (int i = 0; i < chars.length; i++) {
            chars[i] = getRandomLetter('a','z');
        }
        //return the array
        return chars;
    }
    //** display the array of characters */
    public static void displayArray(char[] chars) {
        //display the characters in the array 20 on each line
        for (int i = 0;i < chars.length; i++) {
            if((i+1) % 20 == 0)
                System.out.println(chars[i]);
            else
                System.out.print(chars[i] + " ");
        }
    }
    //** count the occurrences of each letter */
    public static int[] countLetters(char[] chars) {
        //declare and create an array of 26 int
        int[] counts = new int[26];
        //for eac lowercase letter in the array ,count it
        for (int i = 0; i < chars.length; i++)
            counts[chars[i] -'a']++;

        return counts;
    }
    //** create an array of characters */
    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')+" ");
    }

//**get the random chars*/
    public static char getRandomLetter(char ch1,char ch2) {
        return (char)(ch1 + Math.random()* (ch2 - ch1 + 1));
    }
}

7-5 VarArgsDemo.java from page 230

打印出个数不定的列表中最大值的方法

public class demo {
    public static void main(String[] args) {
        printMax(34,3,3,2,56.5);
        printMax(new double[]{1,2,3});
        }
        //
    public static void printMax(double...numbers) {
        if (numbers.length == 0) {
            System.out.println("no argument passed"); //no array passed in
            return;
        }

        double result = numbers[0];

        for ( int i = 0 ; i < numbers.length ; i++)
            if (numbers[i] > result)
                result = numbers[i];

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

7-6 LinearSearch.java from page 231

线性查找法查找关键字，与数组中的元素逐个比较

public class demo {
    public static void main(String[] args) {
        int[] list = {1,4,4,2,5,-3,6,2};
        int i = linearSearch(list,4); //1
        int j = linearSearch(list,-4);//-1
        int k = linearSearch(list,-3);//5
        System.out.println("i = " + i+ ", j = "+ j +", k = "+ k);
    }
        //**the method for finding a key in the list*/
    public static int linearSearch(int[] list, int key) {
        for ( int i = 0 ; i < list.length;i++) {
            if ( key == list[i])
                return i;
        }
        return -1;
    }
}

7-7 BinarySearch.java from page 233

二分查找法，并返回插入位置

public class demo {
    public static void main(String[] args) {
        int[] list = {2,4,7,10,11,45,50,59,60,66,69,70,79};
        int i = BinarySearch(list,2); //0
        int j = BinarySearch(list,11);//4
        int k = BinarySearch(list,12);//-6 -k-1
        int l = BinarySearch(list,1);//-1
        int m = BinarySearch(list,3);//-2
        System.out.println("i = " + i);
        System.out.println("j = " + j);
        System.out.println("k = " + k);
        System.out.println("l = " + l);
        System.out.println("m = " + m);
    }

    //**use binary search to find the key in the list*/
    public static int BinarySearch(int[] list, int key) {
        int low = 0;
        int high = list.length - 1;

        while (high >= low) {
            int mid = (high + low) / 2;
            if (key < list[mid])
                high = mid - 1;
            else if (key==list[mid])
                return mid;
            else
                low = mid + 1;
        }
        return -low-1; //now high < low,key not found
    }
}

7-8 SelectionSort.java from page 235

数字排序（没有解释输出）

public class demo {
    public static void main(String[] args) {
        double[] list = {1,9,4.5,6.6,5.7,-4.5};
        selectionSort(list);
        System.out.println(list);
    }
    /** the method for sorting the numbers*/
    public static double[] selectionSort(double[] list) {
        for (int i = 0; i < list.length; i++) {
            //find the minimum in the list[i..list.length-1]
            double currentMin = list[i];
            int currentMinIndex = i;

            for (int j = i + 1; j < list.length; j++) {
                if (currentMin > list[i]) {
                    currentMin = list[i];
                    currentMinIndex = i;
                }
            }
            //swap list[i] with list[currentMinIndex] if necessary
            if (currentMinIndex != i)
                list[currentMinIndex] = list[i];
                list[i] = currentMin;
        }
        return list;
    }
}

返回地址↑

无返回↓

public class demo {
    public static void main(String[] args) {
        double[] list = {1,9,4.5,6.6,5.7,-4.5};
        selectionSort(list);
    }
    /** the method for sorting the numbers*/
    public static void selectionSort(double[] list) {
        for (int i = 0; i < list.length; i++) {
            //find the minimum in the list[i..list.length-1]
            double currentMin = list[i];
            int currentMinIndex = i;

            for (int j = i + 1; j < list.length; j++) {
                if (currentMin > list[i]) {
                    currentMin = list[i];
                    currentMinIndex = i;
                }
            }
            //swap list[i] with list[currentMinIndex] if necessary
            if (currentMinIndex != i)
                list[currentMinIndex] = list[i];
                list[i] = currentMin;
        }
    }
}

7-9 Calculator.java from page 238（示例学习）

开发程序完成完成两个整数的算术运算

public class demo {
    public static void main(String[] args) {
        //0 check number of strings passed
        if (args.length != 3) {
            System.out.println("usage: java Calculator operand1 operator operand2");
            System.exit(1);
        }
        //1 initialize the result of the operation
        int result = 0;
        //2 determine the operator
        switch (args[1].charAt(0)) {
            case '+':result = Integer.parseInt(args[0])+ Integer.parseInt(args[2]);
                    break;
            case '-':result = Integer.parseInt(args[0])+Integer.parseInt(args[2]);
                    break;
            case '.':result = Integer.parseInt(args[0])+Integer.parseInt(args[2]);
                    break;
            case '/':result = Integer.parseInt(args[0])+Integer.parseInt(args[2]);
                    break;
        }
        //3 display result
        System.out.println(args[0]+' '+args[1]+' '+args[2]+"="+result );
    }
}