Java数组

一、基本概述

• 1.数组是在内存中连续存储多个相同数据类型的元素的结构
• 2.数组的长度固定不变，避免数组越界
• 3.数组的元素通过下标访问，一维数组可用一个循环动态初始化，二维
• 数组可用嵌套循环动态初始化，二维数组可以看做一维数组嵌套的构成
• 4.语法：

　　　　datatype[] arrayName = new datatype[size];
　　　　int[] nums = new int[5];

   　　　int[] nums = {1, 2, 4, 7, 12};　

//循环输出斐波那契数列的值
//求数列中所有数值的和及平均值
public class Fibonaqi {

    public static void main(String[] args) {
        final int N = 20;  
        int[] fibo = new int[N]; //定义一个空的数组，数组长度为20
        int sum = 0;    //数组和
        double avg = 0;  //数组的平均值
        
        //1.构造数组
        fibo[0] = 0;
        fibo[1] = 1;
        for (int i = 2; i < fibo.length; i++) {
            fibo[i] = fibo[i-1] + fibo[i-2];
        }
        //2.输出数组
        for (int i = 0; i < fibo.length; i++) {
            System.out.print(fibo[i] + " ");
            sum += fibo[i];
        }
        //3.计算打印和及平均值
        avg = sum / fibo.length;
        System.out.println();
        System.out.printf("数组和为：%-5d\t平均值为：%-5.2f",sum,avg);
    }
}

//遍历查找求数组的最大值和最小值
public class MaxMinDemo {

    public static void main(String[] args) {
        //1、随机生成一个数组
        final int N = 10;
        int[] nums = new int[N];
        for (int i = 0; i < nums.length; i++) {
            nums[i] = (int) (Math.random()*1000);
            System.out.print(nums[i]+" ");
        }
        
        //2、遍历比较max min
        int max = Integer.MIN_VALUE;
        int min = Integer.MAX_VALUE;
        for (int i = 0; i < nums.length; i++) {
            if(nums[i] > max){
                max = nums[i];
            }
            if(nums[i] < min){
                min = nums[i];
            }
        }
        //3、输出最大值 最小值
        System.out.println("\n最大值是："+max+"\t最小值是："+min);
    }
}

package shuffledemo;

public class ShuffleDemo {

    public static void main(String[] args) {
        String[] cardscolor = {"黑桃","红心","方块","梅花"};
        String[] cardsvalue = {"A","2","3","4","5","6","7",
                "8","9","10","J","Q","K"}; //每种花色13张牌
        final int N = 52;
        int[] cards = new int[N];
        for (int i = 0; i < cards.length; i++) {
            cards[i] = i;
        }
        //洗牌前
        System.out.println("洗牌前：");
        for (int i = 0; i < cards.length; i++) {
            System.out.printf("%s-%s",cardscolor[i / 13],cardsvalue[i % 13]);
            if((i+1) % 13 == 0){
                System.out.println();
            }else{
                System.out.print("\t");
            }
        }
        
        System.out.println("-------------------------------------------------------------------------------------");
        
        //换牌
        System.out.println("洗牌后：");
        for (int i = 0; i < cards.length; i++) {
            int index =(int)( Math.random() * N);
            int temp = cards[i];
            cards[i] = cards[index];
            cards[index] = temp;
        }
        //洗牌后
        for (int i = 0; i < cards.length; i++) {
            System.out.printf("%s-%s",cardscolor[cards[i] / 13],cardsvalue[cards[i] % 13]);
            if((i+1) % 13 == 0){
                System.out.println();
            }else{
                System.out.print("\t");
            }
        }
    }
}

package bubsortdemo;

public class BubsortDemo {

    public static void main(String[] args) {
        // 冒泡正向对数组进行排序
        int[] nums = {67, 49, 66, 46, 22, 9, 90, 11};
        
        //外层循环,它决定一共走几趟
        for (int i = 0; i < nums.length-1; i++) {
            //内层循环,开始逐个比较
            //如果我们发现前一个数比后一个数大,则交换
            for (int j = 0; j < nums.length - i - 1; j++) {
                if(nums[j] > nums[j + 1]){
                    int temp = nums[j];
                    nums[j] = nums[j + 1];
                    nums[j +1] = temp;
                }
            }
        }
        //打印数组
        for (int i : nums) {
            System.out.print(i + ",");
        }
    }

}

package selectionsort;

public class SelectionSort {

    public static void main(String[] args) {
        // 使用选择排序法逆向排序
                int[] nums = {67, 49, 66, 46, 22, 9, 90, 11};
                //内层循环,控制查找的趟数
                for (int i = 0; i < nums.length-1; i++) {
                    
                    //每一次将数组的第一个元素和后面所有的数字比较，如果小于则交换
                    for (int j = i + 1; j < nums.length; j++) {
                        if(nums[i] < nums[j]){
                            int temp = nums[i];
                            nums[i] = nums[j];
                            nums[j] = temp;
                        }
                    }
                }
                //打印数组
                for (int i : nums) {
                    System.out.print(i + ",");
                }
    }

}

import java.util.Arrays;

public class SelectionSort {

    public static void main(String[] args) {
        // 使用java.util.Arrays.sort()方法进行排序
        int[] nums = {67, 49, 66, 46, 22, 9, 90, 11};
        Arrays.sort(nums);
        //打印数组
        for (int i : nums) {
            System.out.print(i + ",");
        }                        
    }
}