java数组

本文详细介绍了数组的基本概念,包括定义、初始化、使用等步骤,并通过多个案例演示了如何进行数组的遍历、查找、修改、删除及排序等操作,同时讲解了二维数组的应用。

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数组

1. 定义

数组就是同一类型的一组数的有序集合,并且个数有限。

2. 定义数组步骤:

  1. 声明

    int[] a;//在栈内存中开辟,用于存放数组在堆内存中的地址
    
  2. 开辟空间

    a[] = new int[5];
    
  3. 赋值

    a[1] = 10;
    
  4. 使用

    a[1]+=a[1];
    

3.案例

  1. 案例1计算平均分(数组增加)

    	public static void main(String[] args) {
    		int b[] = new int[] {1,2,3,4,5};
    		int sum = 0;
    		for(int i = 0; i < b.length;i++) {
    			sum+= b[i];
    		}
    		System.out.println("平均分是:" + sum/(b.length*1.0));
    //		int[] a= {1 ,23,54,6,56};
    //		for(int i = 0;i<a.length;i++) {
    //			System.out.println(a[i]);
    //		}
    //		声明和初始化必须在一行,否者会报错。
    		
    		
    	}
    }
    
  2. 案例foreach遍历数组

    public static void main(String[] args) {
    		Scanner in = new Scanner(System.in);
    		int score[] = new int[5];
    		int sum = 0;
    		for(int i = 0;i<score.length;i++) {
    			System.out.println("请输入第" + (i+1) + "个同学的分数:");
    			score[i] = in.nextInt();
    			sum += score[i];
    		}
    		//foreach或者叫加强for循环
    		//注意:foreach只能用于数组或集合的遍历
    		for (int i : score) {
    			System.out.print(" " + i);
    		}
    		double avg = sum/score.length*1.0;
    		System.out.println("五个同学的平均分是:" + avg);
    	}
    
  3. 案例3通过数组找人(数组查找)

    public static void main(String[] args) {
    		Scanner in = new Scanner(System.in);
    		String userName[] = new String[6];
    		for(int i = 0;i<userName.length;i++) {
    			System.out.println("请输入第" + i + "个姓名:");
    			userName[i] = in.next();
    			
    		}
    		boolean flag = false;
    		System.out.println("请输入要寻找的姓名:");
    		String findName = in.next();
    		for(int i = 0;i<userName.length;i++) {
    			if(userName[i].equals(findName)) {
    				
    				flag = true;
    				break;
    			}
    			
    		}
    		if(flag) {
    			System.out.println("找到" + findName);
    		}else {
    			System.out.println("没有找到" + findName);
    		}
    		
    			
    	
    	}
    
  4. 案例4修改书名(数组修改)

    public static void main(String[] args) {
    		Scanner in = new Scanner(System.in);
    		String books[] = new String[4];
    		System.out.println("请输入书名:");
    		String nowName = in.next();
    		books[0] = "三国演义";
    		books[1] = "西游记";
    		for(int i = 0;i<books.length;i++) {
    			if(books[i] == null) {
    				books[i] =  nowName;
    				break;
    			}
    		}
    		System.out.println("*************************");
    		for (int i =0 ;i<books.length;i++) {
    			if("西游记".equals(books[i])) {
    				books[i] = "东游记";
    				break;
    			}
    			
    		}
    		for (String book : books) {
    			if(book != null) {
    				System.out.println(book);
    			}
    		}
    	}
    
  5. 案例5删除书名(数组删除)

    	Scanner in = new Scanner(System.in);
    		String books[]={"万古神帝","挪威森林","三体","伏天氏"};
    		boolean isFind = false;//判断是否找到
    		int index = -1;//找到的电视剧名的索引
    		for (String book : books) {
    			System.out.print(" " + book);
    		}
    		System.out.println("请输入要删除的书名:");
    		String delBook = in.next();
    		for(int i = 0;i<books.length;i++) {
    			if(books[i] != null) {
    				if(delBook.equals(books[i])) {
    					index = i;
    					isFind = true;
    				}
    			}
    			
    		}
    		if(isFind) {
    			for(int i = index;i<books.length-1;i++) {
    				books[i] = books[i+1];
    			}
    			books[books.length-1] = null;
    			System.out.println("\n********************");
    			for (String book : books) {
    				System.out.print(" "+book);
    			}
    		}else {
    			System.out.println("很遗憾,没有找到");
    		}
    		
    			
    		
    	}
    
  6. 案例6比较最大值最小值(数组比较)

    public static void main(String[] args) {
    		Scanner in = new Scanner(System.in);
    		int sum = 0;
    		int su[] = new int[6];
    		for(int i = 0; i < su.length;i++) {
    			System.out.println("请输入第" + (i+1) + "个数:");
    			int score = in.nextInt();
    			su[i]  = score;
    			sum +=su[i];
    		}
    		int max = su[0];
    		int min = su[0];
    		for (int i = 0;i< su.length-1;i++) {
    			if(su[i]>max) {
    				max = su[i];
    			}
    		}
    		for (int i = 0;i< su.length-1;i++) {
    			if(su[i]<min) {
    				min = su[i];
    			}
    		}
    		double avg = sum/(su.length*1.0);
    		System.out.println("最大值是:" + max + "\t最小值是" + min + "\t总分是:" + sum + "\t平均分是:" + avg);
    	}
    

4. 数组排序

  1. 冒泡排序

    public static void main(String[] args) {
    		int array[] = {47,58,96,32,14,45};
    		for (int i = 0; i < array.length-1; i++) {
    			for (int j = 0; j < array.length-i-1; j++) {
    				if (array[j]<array[j+1]) {
    					int temp = array[j];
    					array[j] = array[j+1];
    					array[j+1] = temp;
    				}
    			}	
    		}
    		for (int a : array) {
    			System.out.print(" " + a);
    		}
    	}
    
  2. 其他排序

  3. i++和++i的区别

    • i++先计算后自增

      int a=10;
      int b = a+++5;
      System.out.println("a="+a);
      System.out.println("b="+a);
      
      结果
      a=11
      b=15
      
    • ++i先自增后计算

      int a=10;
      int b = ++a+5;
      System.out.println("a="+a);
      System.out.println("b="+a);
      
      结果
      a=11
      b=16
      

5.二维数组和二重循环

  1. 定义二维数组

    	Scanner in = new Scanner(System.in);
    		//定义二维数组
    		int score[][] = new int[3][4];
    		
    		for (int  i = 0; i < score.length;i ++) {
    			System.out.println("****************第" + (i+1) + "班*************************");
    			int sum = 0;
    			for (int  j= 0; j < score[i].length; j++) {
    				System.out.print("第" + (i+1) +"班第"  + (j+1) + "个同学的分数::");
    				score[i][j] = in.nextInt();
    				sum += score[i][j];
    			}
    			double avg = sum/(score[i].length*1.0);
    			System.out.println("第" + (i+1) + "班的平均分:" + avg);
    		}
    		for (int i = 0; i < score.length; i++) {
    			for (int j = 0; j < score[i].length; j++) {
    				System.out.println(score[i][j]);
    			}
    		}
    
  2. 应用

    Scanner in = new Scanner(System.in);
    		//定义二维数组
    		int score[][] = new int[3][4];
    		for (int  i = 0; i < score.length;i ++) {
    			for (int  j= 0; j < score[i].length; j++) {
    				System.out.print("第" + (i+1) +"班第"  + (j+1) + "个同学的分数:");
    				score[i][j] = in.nextInt();
    			}
    		}
    		int count = 0;
    		for (int i = 0; i < score.length; i++) {
    			for (int j = 0; j < score[i].length; j++) {
    				if(score[i][j]>80) {
    					count++;
    				}
    			}
    		}
    		System.out.println("大于80分的有" +count+"人");
    
    	}
    
  3. 案例

    	Scanner in = new Scanner(System.in);
    		//判断是否买了衣服
    		String pan = "";
    		//记录买了多少件
    		int count = 0;
    		//记录一家店买了多少件衣服
    		int s = 0;
    		for (int i = 1; i <= 5; i++) {
    			System.out.println("欢迎光临第" + i + "家专卖店");
    			do {
    				System.out.print("要离开吗(y/n)?");
    				pan = in.next();
    				if("n".equals(pan)) {
    					System.out.println("买了一件衣服!");
    					count++;
    					s++;
    				}
    			} while ("n".equals(pan)&& s<3);
    			System.out.println("离店结账");
    			System.out.println();
    		}
    		System.out.println("总共买了" + count + "件衣服");
    	}
    
  4. 99乘法表

    for (int i = 1; i <= 9; i++) {
    			for (int j = 1; j <= i; j++) {
    				System.out.print(j + "*" + i + "=" + (i*j) + "\t");
    			}
    		System.out.println();
    		}
    

6.练习1

	Scanner  in = new Scanner(System.in);
		String DVDName[] = new String[100];//存储DVD名字
		int sta[] = new int[100];//记录DVD状态0表示借出,1表示可借
		String DVDData[] = new String[100];//记录DVD借出时间
		//DVD原始数据
		DVDName[0] = "英雄本色";
		sta[0] = 0;
		DVDData[0] = "2020-08-12";
		
		DVDName[1] = "三国演义";
		sta[1] = 1;
		DVDData[1] = "";
		
		DVDName[2] = "穿越火线";
		sta[2] = 0;
		DVDData[2] = "2020-08-01";
		
		DVDName[3] = "二十不惑";
		sta[3] = 1;
		DVDData[3] = "";
		int an=0;
		do {
		 System.out.println("欢 迎 使 用 迷 你 DVD 管 理 器");
   	   	 System.out.println("-------------------------------------");
   	   	 System.out.println("1. 新 增 DVD");
   	   	 System.out.println("2. 查 看 DVD");
   	   	 System.out.println("3. 删 除 DVD");
   	   	 System.out.println("4. 借 出 DVD");
   	     System.out.println("5. 归 还 DVD");
   	   	 System.out.println("6. 退         出 ");
   	   	 System.out.print("--------------------------------------\n");
   	   	 System.out.print("请选择: ");
   	   	 int choice = in.nextInt();
		 switch (choice) {
		 		case 1:
		 			System.out.println("---> 新 增 DVD\n");
		 			for (int i = 0; i < DVDName.length; i++) {
		 				if(DVDName[i] == null) {
		 					System.out.print("请输入DVD名称:");
				 			DVDName[i] = in.next();
				 			sta[i] = 1;
				 			System.out.println("新增《" + DVDName[i] + "》成功!");
				 			System.out.println("**********************");
				 			break;
		 				}
			 			
					}
		 			System.out.print("输入0返回:");
		 			an = in.nextInt();
		 			 if(an != 0) {
		 				System.out.println("输入错误请重新输入:");
		 				an=0;
		 			 }
		 			break;
		 		case 2:
		 			System.out.println("---> 查看 DVD\n");
		 			System.out.println("序号\t状态\t名称\t借出日期");
		 			for (int i = 0; i < DVDName.length; i++) {
						if(DVDName[i] !=null) {
							if(sta[i] ==0) {
								System.out.println((i+1) + "\t借出\t" + DVDName[i] + "\t" + DVDData[i]);
							}else {
								System.out.println((i+1) + "\t可借\t" + DVDName[i] + "\t" + DVDData[i]);
							}
						}
					}
		 			System.out.print("输入0返回:");
		 			an = in.nextInt();
		 			 if(an != 0) {
		 				System.out.println("输入错误请重新输入:");
		 				an=0;
		 			 }
		 			break;
		 		case 3:
		 			System.out.println("---> 删除 DVD\n");
		 			boolean falg = true;
		 			do {
		 				int index=0;
		 				System.out.print("请输入DVD名称:");
				 		String delDVD = in.next();
				 		for (int i = 0; i < DVDName.length-1; i++) {
				 			if(delDVD.equals(DVDName[i])&&DVDName != null) {
				 				if(sta[i] == 1) {
				 					index = i; 
					 				falg = false;
					 				while (DVDName[index+1] != null) {
							 			DVDName[index] = DVDName[index+1];
							 			sta[index] = sta[index+1];
							 			DVDData[index] = DVDData[index+1];
									}
							 		DVDName[i] = null;
							 		System.out.println("删除《" + delDVD + "》成功");
				 				}else {
				 					System.out.println("已借出,不能删除");
				 				}
				 				
				 			}
				 			
				 		}
				 		if(falg) {
				 			System.out.println("没有找到匹配信息!");
				 			System.out.println("**************************");
				 			break;
				 		}
				 		
				 	
				 		
					} while (falg);
		 			System.out.print("输入0返回:");
		 			an = in.nextInt();
		 			 if(an != 0) {
		 				System.out.println("输入错误请重新输入:");
		 				an=0;
		 			 }
					break;
		 		case 4:
		 			System.out.println("---> 借出DVD\n");
		 			System.out.print("请输入DVD名称:");
			 		String selDVD = in.next();
			 		falg =true;
		 			for (int i = 0; i < DVDName.length; i++) {
		 				
				 		if(selDVD.equals(DVDName[i])&&DVDName[i]!=null) {
				 			if (sta[i] ==1) {
				 				sta[i] = 0;
				 				falg = false;
					 			System.out.println("请输入借出日期(年-月-日):");
					 			DVDData[i] = in.next();
							}else {
								System.out.println("DVD已借出");
								break;
							}
				 		}
					}
		 			if(falg){
			 			System.out.println("没有该DVD");
			 			break;
			 		}else {
			 			System.out.println("借出成功!");
			 		}
		 			
		 			System.out.print("输入0返回:");
		 			an = in.nextInt();
		 			 if(an != 0) {
		 				System.out.println("输入错误请重新输入:");
		 				an=0;
		 			 }
		 			break;
		 		case 5:
		 			System.out.println("---> 归还DVD\n");
		 			System.out.print("请输入DVD名称:");
			 		String inDVD = in.next();
		 			for (int i = 0; i < DVDName.length; i++) {
		 				
				 		if(inDVD.equals(DVDName[i])&&DVDName[i]!=null&&sta[i] == 0) {
				 			sta[i] = 1;
				 			System.out.println("请输入借出日期(年-月-日):");
				 			DVDData[i] = in.next();
				 		}
					}
		 			System.out.println("\n谢谢使用");
		 			System.out.print("输入0返回:");
		 			an = in.nextInt();
		 			 if(an != 0) {
		 				System.out.println("输入错误请重新输入:");
		 				an=0;
		 			 }
		 			break;
		 		case 6:
		 			an = 1;
		 			System.out.println("谢谢使用!");
		 		    break;
		 		default:
		 			System.out.println("输入错误:");
		 			break;
		 	}
		
		} while (an == 0);
	}	
	

7.练习2

	// 数据主体:一组订单信息
		String[] names = new String[4]; // 订餐人名称
		String[] dishMegs = new String[4]; // 所选菜品
		int[] times = new int[4]; // 送餐时间
		String[] addresses = new String[4]; // 送餐地址
		int[] states = new int[4]; // 订单状态: 0:已预定 1:已完成
		double[] sumPrices = new double[4]; // 总金额
		
		//初始化2个订单信息
		names[0] = "张晴";
		dishMegs[0] = "红烧带鱼 2份";
		times[0] = 12;
		addresses[0] = "天成路207号";
		sumPrices[0] = 76.0;
		states[0] = 1;
		
		names[1] = "张晴";
		dishMegs[1] = "鱼香肉丝 2份";
		times[1] = 18;
		addresses[1] = "天成路207号";
		sumPrices[1] = 20.0;
		
		
		// 供选择的菜品信息
		String[] dishNames = { "红烧带鱼", "鱼香肉丝", "时令鲜蔬" }; // 菜品名称
		double[] prices = new double[] { 38.0, 20.0, 10.0 }; // 菜品单价
		int[] praiseNums = new int[3];

		Scanner input = new Scanner(System.in);
		int num = -1; // 用户输入0返回主菜单,否则退出系统
		boolean isExit = false; // 标志用户是否退出系统: true:退出系统

		System.out.println("\n欢迎使用“吃货联盟订餐系统”");
		// 循环:显示菜单,根据用户选择的数字执行相应功能
		do {
			// 显示菜单			
			System.out.println("****************************");
			System.out.println("1、我要订餐");
			System.out.println("2、查看餐袋");
			System.out.println("3、签收订单");
			System.out.println("4、删除订单");
			System.out.println("5、我要点赞");
			System.out.println("6、退出系统");
			System.out.println("****************************");
			System.out.print("请选择:");
			int choose = input.nextInt(); // 记录用户选择的功能编号
			boolean isAdd = false;  //记录是否可以订餐
			boolean isSignFind = false;  //找到要签收的订单
			boolean isDelFind = false;  //找到要删除的订单
			// 根据用户选择的功能编号执行相应功能
			switch (choose) {
			case 1:
				// 我要订餐
				System.out.println("***我要订餐***");
				for (int j = 0; j < names.length; j++) {					
                   if(names[j] == null){  //找到第一个空位置,可以添加订单信息
                	   isAdd = true;  //置标志位,可以订餐
                	   System.out.print("请输入订餐人姓名:");
   					String name = input.next(); 
					// 显示供选择的菜品信息
					System.out.println("序号" + "\t" + "菜名"+"\t"+"单价");
					for (int i = 0; i < dishNames.length; i++) {
						String price = prices[i] + "元";
						String priaiseNum = (praiseNums[i]) > 0 ? praiseNums[i]
								+ "赞" : "";
						
						System.out.println((i + 1) + "\t" + dishNames[i] + "\t"	+price+"\t"+ priaiseNum);
					}
					// 用户点菜
					System.out.print("请选择您要点的菜品编号:");
					int chooseDish = input.nextInt();
					System.out.print("请选择您需要的份数:");
					int number = input.nextInt();
					String dishMeg =  dishNames[chooseDish - 1]
							+" "+ number + "份";
					double sumPrice = prices[chooseDish - 1] * number;
					//餐费满50元,免送餐费10元
					double deliCharge = (sumPrice>=50)?0:6;                   

					System.out.print("请输入送餐时间(送餐时间是10点至20点间整点送餐):");
					int time = input.nextInt();
					while (time < 10 || time > 20) {
						System.out.print("您的输入有误,请输入10~20间的整数!");
						time = input.nextInt();
					}
					System.out.print("请输入送餐地址:");
					String address = input.next();
										
					//无需添加状态,默认是0,即已预定状态。
					System.out.println("订餐成功!");
					System.out.println("您订的是:"+dishMeg);
					System.out.println("送餐时间:"+time+"点");
					System.out.println("餐费:"+sumPrice+"元,送餐费"+deliCharge+"元,总计:"+(sumPrice+deliCharge)+"元。");
					
					//添加数据
					names[j] = name;
					dishMegs[j] = dishMeg;
					times[j] = time;
					addresses[j] = address;
					sumPrices[j] = sumPrice+deliCharge;
					
					break;					
                   }
				}
				if(!isAdd){
					System.out.println("对不起,您的餐袋已满!");
				}
				break;
			case 2:
				// 查看餐袋
				System.out.println("***查看餐袋***");
				System.out.println("序号\t订餐人\t餐品信息\t\t送餐日期\t送餐地址\t\t总金额\t订单状态");
				for(int i=0;i<names.length;i++){
					if(names[i]!=null){  
						String state = (states[i]==0)?"已预定":"已完成";
						String date = times[i]+"日";
						String sumPrice = sumPrices[i]+"元";
						System.out.println((i+1)+"\t"+names[i]+"\t"+dishMegs[i]+"\t"+date+"\t"+addresses[i]+"\t"+sumPrice+"\t"+state);
					}
				}
				break;
			case 3:
				// 签收定单
				System.out.println("***签收定单***");
				System.out.print("请选择要签收的订单序号:");
				int signOrderId = input.nextInt();
				for(int i=0;i<names.length;i++){
					//状态为已预定,序号为用户输入的订单序号:可签收
					//状态为已完成,序叼为用户输入胡订单序号:不可签收					
					if(names[i]!=null && states[i]==0 && signOrderId==i+1){
						states[i] = 1; //将状态值置为已完成
						System.out.println("订单签收成功!");
						isSignFind = true;
					}else if(names[i]!=null && states[i]==1 && signOrderId==i+1){
						System.out.println("您选择的订单已完成签收,不能再次签收!");
						isSignFind = true;
					}
				}
				//未找到的订单序号:不可签收
				if(!isSignFind){
					System.out.println("您选择的订单不存在!");
				}
				break;
			case 4:
				// 删除订单
				System.out.println("***删除订单***");
				System.out.print("请输入要删除的订单序号:");
				int delId = input.nextInt();
				for(int i=0;i<names.length;i++){
					//状态值为已完成  序号值为用户输入的序号:可删除
					//状态值为已预定  序号值为用户输入的序号:不可删除
					if(names[i]!=null && states[i]==1 && delId==i+1){	
						isDelFind = true;
						//执行删除操作:删除位置后的元素依次前移
						for(int j=delId-1;j<names.length-1;j++){
							names[j] = names[j+1];
							dishMegs[j] = dishMegs[j+1];
							times[j] = times[j+1];
							addresses[j] = addresses[j+1];
							states[j] = states[j+1];
						}
						//最后一位清空
						names[names.length-1] = null;
						dishMegs[names.length-1] = null;
						times[names.length-1] = 0;
						addresses[names.length-1] = null;
						states[names.length-1] = 0;
						
						System.out.println("删除订单成功!");
						break;
					}else if(names[i]!=null && states[i]==0 && delId==i+1){
						System.out.println("您选择的订单未签收,不能删除!");
						isDelFind = true;
						break;
					}
				}
				
				//未找到该序号的订单:不能删除
				if(!isDelFind){
					System.out.println("您要删除的订单不存在!");
				}							
				break;
			case 5:
				// 我要点赞
				System.out.println("***我要点赞***");
				// 显示菜品信息
				System.out.println("序号" + "\t" + "菜名"+"\t"+"单价");
				for (int i = 0; i < dishNames.length; i++) {
					String price = prices[i] + "元";
					String priaiseNum = (praiseNums[i]) > 0 ? praiseNums[i]
							+ "赞" : "0赞";
					
					System.out.println((i + 1) + "\t" + dishNames[i] + "\t"	+price+"\t"+ priaiseNum);
				}
				System.out.print("请选择您要点赞的菜品序号:");
				int priaiseNum = input.nextInt();
				praiseNums[priaiseNum-1]++;  //赞数加1
				System.out.println("点赞成功!");
				break;
			case 6:
				// 退出系统
				isExit = true;
				break;
			default:
				//退出系统
				isExit = true;
				break;
			}
			if (!isExit) {
				System.out.print("输入0返回:");
				num = input.nextInt();
			} else {
				break;
			}
		} while (num == 0);
		System.out.println("谢谢使用,欢迎下次光临!");
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