Java基础学习Day04

谁借莪１个温暖的怀抱￠ 2021-11-08 23:38 285阅读 0赞

#### 知识点 ####

1.  方法的重载
2.  数组
3.  内存

##### 方法的重载 #####

overload(重载)

1.  参数名相同
2.  参数列表不同

##### 数组 #####

1.  静态数组初始化  
    int\[\] arr = new int\[\]\{1, 2, 3, 4, 5\};
2.  动态数组初始化  
    int\[\] arr = new int\[5\];

##### 内存 #####

1.  常量池  
    存放常量
2.  静态域  
    存放静态数据
3.  栈  
    存放变量和引用
4.  堆  
    存放new出来的数据

#### 课后作业 ####

1.  用数组存放7个数据后进行排序

package com.day04;
    
    public class Array {
        
    	public static void main(String[] args) {
        
    		int[] arr = new int[]{
        2, 4, 9, 5, 7};
    		int max = arr[0];
    		
    		for(int i = 1; i < arr.length; i++) {
        
    			if(max < arr[i]) {
        
    				max = arr[i];
    			}
    		}
    		
    		System.out.println(max);
    	}
    }

1.  给7个数据进行排序

package com.day04;
    
    import java.util.Arrays;
    
    public class Test01 {
        
    	public static void main(String[] args) {
        
    		int[] arr = new int[]{
        1, 3, 5, 2, 7, 3, 8};
    		
    		//冒泡排序
    		for(int i = 0; i < arr.length - 1; i++) {
        
    			for(int j = 0; j < arr.length - i - 1; j++) {
        
    				int temp;
    				if(arr[j] > arr[j + 1]) {
        
    					temp = arr[j];
    					arr[j] = arr[j + 1];
    					arr[j + 1] = temp;
    				}
    			}
    		}
    		System.out.println(Arrays.toString(arr));
    	
    		//选择排序
    		for(int i = 0; i < arr.length - 1; i++) {
        
    			for(int j = i; j < arr.length - 1; j++) {
        
    				int temp;
    				if(arr[i] > arr[j + 1]) {
        
    					temp = arr[i];
    					arr[i] = arr[j + 1];
    					arr[j + 1] = temp;
    				}
    			}
    		}
    		System.out.println(Arrays.toString(arr));
    	}
    }

1.  折半查找

package com.day04;
    
    public class HalfQuery {
        
    	public static void main(String[] args) {
        
    		int[] arr = new int[]{
        2, 4, 9, 15, 27};
    		System.out.println(HalfQuery(arr, 27));
    	}
    	
    	public static int HalfQuery(int[] arr, int val) {
        
    		int length = arr.length;
    		int front = 0;
    		int rear = length - 1;
    		int mid;
    		while(front <= rear) {
        
    			mid = (front + rear) / 2;
    			if(val == arr[mid]) {
        
    				return mid;
    			}
    			else if(arr[mid] < val) {
        
    				front = mid + 1;
    			}
    			else if(arr[mid] > val) {
        
    				rear = mid - 1;
    			}
    		}
    		return -1;
    	}
    }

1.  注册登录系统

package com.day04;
    
    import java.util.Scanner;
    
    public class Test03 {
        
    	private static int n = 5;
    	private static Scanner sca = new Scanner(System.in);
    	private static int length = 0;
    	private static String[][] data = new String[n][];
    	
    	public static void main(String[] args) {
        
    		menu1();
    	}
    	
    	//登陆菜单
    	static void menu1() {
        
    		System.out.println("欢迎使用夜雨柠檬的系统");
    		System.out.println("1. 登陆");
    		System.out.println("2. 注册");
    		System.out.println("0. 退出");
    		
    		int p = sca.nextInt();
    		if(p == 1) {
        
    			login();
    		}
    		if(p == 2) {
        
    			register();
    		}
    		if(n == 0) {
        
    			return;
    		}
    	}
    	
    	//操作菜单
    	static void menu2() {
        
    		System.out.println("欢迎进入夜雨柠檬内部系统！");
    		System.out.println("1. 添加会员");
    		System.out.println("2. 删除会员");
    		System.out.println("3. 查询会员");
    		System.out.println("4. 更改会员");
    		System.out.println("0. 退出");
    		
    		int p = sca.nextInt();
    		if(p == 1) {
        
    			add();
    		}
    		if(p == 2) {
        
    			delete();
    		}
    		if(p == 3) {
        
    			query();
    		}
    		if(p == 4) {
        
    			change();
    		}
    		if(n == 0) {
        
    			return;
    		}
    	}
    	
    	//登陆
    	static void login() {
        
    		System.out.print("请输入用户名：");
    		String username = sca.next();
    		System.out.print("请输入密码：");
    		String userpassword = sca.next();
    		for(int i = 0; i < length; i++) {
        
    			if(data[i][0].equals(username) && data[i][1].equals(userpassword)) {
        
    				System.out.println("登陆成功！");	
    				menu2();
    				menu1();
    				return;
    			}
    		}
    		System.out.println("登陆失败！");
    		login();
    	}
    	
    	//注册
    	static void register() {
        
    		if(length == n) {
        
    			System.out.println("会员已满");
    			menu1();
    			return;
    		}
    		data[length] = new String[2];
    		System.out.print("请输入会员名：");
    		data[length][0] = sca.next();
    		System.out.print("请输入密码：");
    		data[length][1] = sca.next();
    		length++;
    		System.out.println("注册成功！");
    		menu1();
    		return;
    	}
    	
    	//添加
    	static void add() {
        
    		if(length == n) {
        
    			System.out.println("会员已满");
    			menu2();
    			return;
    		}
    		data[length] = new String[2];
    		System.out.print("请输入会员名：");
    		data[length][0] = sca.next();
    		System.out.print("请输入密码：");
    		data[length][1] = sca.next();
    		length++;
    		System.out.println("添加成功！");
    		menu2();
    		return;
    	}
    	
    	//删除
    	static void delete() {
        
    		if(length == 0) {
        
    			System.out.println("数据为空！");
    		}
    		System.out.print("请输入用户名：");
    		String username = sca.next();
    		for(int i = 0; i < length; i++) {
        
    			if(data[i][0].equals(username)) {
        
    				for(int j = i; j < length - 1; j++) {
        
    					data[j] = data[j + 1];				
    				}
    				length--;
    				System.out.println("删除成功！");
    				menu2();
    				return;
    			}
    		}
    		System.out.println("删除失败！");
    		delete();
    	}
    	
    	//查询
    	static void query() {
        
    		if(length == 0) {
        
    			System.out.println("数据为空！");
    		}
    		System.out.print("请输入用户名：");
    		String username = sca.next();
    		for(int i = 0; i < length; i++) {
        
    			if(data[i][0].equals(username)) {
        
    				System.out.printf("%s\t", data[i][0]);
    				System.out.printf("%s\n", data[i][1]);
    				menu2();
    				return;
    			}
    		}
    		System.out.println("查询失败！");
    		query();
    	}
    	
    	//更改会员
    	static void change() {
        
    		if(length == 0) {
        
    			System.out.println("数据为空！");
    		}
    		System.out.print("请输入要更改会员名：");
    		String username = sca.next();
    		
    		for(int i = 0; i < length; i++) {
        
    			if(data[i][0].equals(username)) {
        
    				System.out.print("会员名将要改为：");
    				username = sca.next();
    				data[i][0] = username;
    				System.out.print("密码将要改为：");
    				String userpassword = sca.next();
    				data[i][1] = userpassword;
    				System.out.println("更改成功！");
    				menu2();
    				return;
    			}
    		}
    		System.out.println("更改失败！");
    		change();
    	}
    }