5、程序控制结构

程序控制结构

1、介绍

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2、顺序控制

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3、分支控制 if-else

image-20210710211912272

3.1、单分支

image-20210710213032116

import java.util.Scanner;
public class If01 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.println("请输入年龄：");
		//把年龄保存到一个变量
		int age = sc.nextInt();
		if (age > 18) {
			System.out.println("你年龄大于18，要对自己的行为负责，送入监狱");
		} else {
			System.out.println("你还是未成年，好好读书");
		}
	}
}

image-20210710213130768

image-20210710213343391

3.2、双分支

image-20210710213435039

import java.util.Scanner;
public class If02 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.println("请输入年龄：");
		//把年龄保存到一个变量
		int age = sc.nextInt();
		if (age > 18) {
			System.out.println("你年龄大于18，要对自己的行为负责，送入监狱");
		} else {
			System.out.println("你的年龄不大这次放过你了");
		}
	}
}

image-20210710213817078

image-20210710213936843

3.3、单分支和双分支练习题

image-20210710214440885

image-20210710220200941

**2: **

import java.util.Scanner;
public class IfExercise01 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.println("请输入第一个数：");
		double d1 = sc.nextDouble();
		System.out.println("请输入第二个数：");
		double d2 = sc.nextDouble();

		if (d1 > 10.0 && d2 < 20.0) {
			System.out.println(d1 + d2);
		} else {
			System.out.println("程序继续...");
		}
	}
}

image-20210710220246534

**3: **

import java.util.Scanner;
public class IfExercise02 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.println("请输入第一个数：");
		int n1 = sc.nextInt();
		System.out.println("请输入第二个数：");
		int n2 = sc.nextInt();
		int sum = n1 + n2;

		if ( sum % 3 == 0 && sum % 5 == 0) {
			System.out.println(sum + "能被3和5整除");
		} else {
			System.out.println(sum + "不能被3和5整除");
		}
	}
}

image-20210710220328667

**4: **

import java.util.Scanner;
public class IfExercise03 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.println("请输入一个年份：");
		int year = sc.nextInt();

		if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
			System.out.println(year + "是闰年");
		} else {
			System.out.println(year + "不是闰年");
		}
	}
}

image-20210710221543394

3.4、多分支

image-20210710222301269

image-20210710222024786

image-20210710222938953

import java.util.Scanner;
public class If03 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.println("请输入芝麻信用分(1-100)：");
		int score = sc.nextInt();

		//对输入的信用分，进行一个范围的有效判断
		if ( score <= 100 && score > 0 ) {
			if (score == 100) {
				System.out.println("信用极好");
			} else if (score > 80 && score <= 99) {
				System.out.println("信用优秀");
			} else if (score >= 60 && score <= 80) {
				System.out.println("信用一般");
			} else {
				System.out.println("信用不及格");
			}
		} else {
			System.out.println("信用分需要在1-100，请重新输入");
		}
		
	}
}

image-20210710223735611

image-20210710224005187

答案是：b

image-20210710224254581

4、嵌套分支

image-20210710224516871

image-20210710225432843

import java.util.Scanner;
public class NestedIf {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.println("请输入初赛成绩：");
		double score = sc.nextDouble();

		if (score > 8.0) {
			System.out.println("恭喜你进入决赛");
			System.out.println("请输入性别：");
			//取第一个字符
			char gender = sc.next().charAt(0);
			if (gender == '男') {
				System.out.println("进入男生组");
			} else if (gender == '女') {
				System.out.println("进入女生组");
			} else {
				System.out.println("性别输入错误，请重新输入");
			}
		} else {
			System.out.println("不好意思，你被淘汰了");
		}
	}
}

image-20210710230137039

image-20210710230253291

import java.util.Scanner;
public class NestedIf02 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.println("请输入你的年龄：");
		int age = sc.nextInt();
		System.out.println("请输入出游的月份：");
		int month = sc.nextInt();

		//定义旺季成人的票价
		int price = 60;
		if (age > 0 && age < 18) {
			if (month >= 4 && month <= 10) {
				System.out.println("儿童票价为" + (price * (1.0 / 2)));
			} else {
				System.out.println("儿童票价为" + 20);
			}
		} else if (age >= 18 && age <= 60) {
			if (month >= 4 && month <= 10) {
				System.out.println("成人票价为" + price);
			} else {
				System.out.println("成人票价为" + 40);
			}
		} else if (age > 60) {
			if (month >= 4 && month <= 10) {
				System.out.println("老人票价为" + (price * (1.0 / 3)));
			} else {
				System.out.println("老人票价为" + 20);
			}
		} else {
			System.out.println("年龄输入错误，请重新输入");
		}
	}
}

image-20210710231952558

5、switch分支结构

5.1、基本语法

image-20210711102233021

5.2、流程图

image-20210711102717881

5.3、快速入门

image-20210711104448793

import java.util.Scanner;
public class Switch01 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		System.out.println("请输入一个字符(a-g)：");
		char c = sc.next().charAt(0);

		switch(c) {
			case 'a':
				System.out.println("星期一");
				break;
			case 'b':
				System.out.println("星期二");
				break;
			case 'c':
				System.out.println("星期三");
				break;
			case 'd':
				System.out.println("星期四");
				break;
			case 'e':
				System.out.println("星期五");
				break;
			case 'f':
				System.out.println("星期六");
				break;
			case 'g':
			    System.out.println("星期日");
			    break;
			default:
				System.out.println("输入错误，请重新输入");
		}
	}
}

image-20210711104529180

5.4、注意事项与细节

image-20210711142447387

image-20210711142507514

5.5、课堂练习

image-20210711142324751

**1: **

import java.util.Scanner;public class SwitchExercise01 {	public static void main(String[] args) {		Scanner sc = new Scanner(System.in);		System.out.println("请输入一个字符(a-e)：");		char c = sc.next().charAt(0);		switch (c) {			case 'a':				System.out.println("A");				break;			case 'b':				System.out.println("B");				break;				case 'c':				System.out.println("C");				break;			case 'd':				System.out.println("D");				break;			case 'e':				System.out.println("E");				break;			default:				System.out.println("other");		}	}}

image-20210711143346679

**2: **

import java.util.Scanner;public class SwitchExercise02 {	public static void main(String[] args) {		Scanner sc = new Scanner(System.in);		System.out.println("请输入学生成绩(0-100)：");		double score = sc.nextDouble();		//如果成绩在 [60,100]，(int)(成绩/60) = 1		//如果成绩在 [0,60)，(int)(成绩/60) = 0		if (score >= 0 && score <= 100) {			switch ((int)(score / 60)) {				case 0:					System.out.println("不合格");					break;				case 1:					System.out.println("合格");					break;			}		} else {			System.out.println("输入错误，请重新输入");		}	}}

image-20210711143502090

**3: **

import java.util.Scanner;public class SwitchExercise03 {	public static void main(String[] args) {		Scanner sc = new Scanner(System.in);		System.out.println("请输入月份(1-12)：");		int month = sc.nextInt();		switch (month) {			case 3:			case 4:			case 5:				System.out.println("春季");				break;			case 6:			case 7:			case 8:				System.out.println("夏季");				break;			case 9:			case 10:			case 11:				System.out.println("秋季");				break;			case 12:			case 1:			case 2:				System.out.println("冬季");				break;			default:				System.out.println("输入错误，请重新输入");		}	}}

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5.6、switch和if的比较

image-20210711145247785

6、for循环控制

6.1、基本介绍

image-20210711145810461

6.2、基本语法

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6.3、执行流程分析

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6.4、注意事项和细节说明

image-20210711152324855

public class ForDetail {
	public static void main(String[] args) {
		int count = 3;

		/* 执行流程
		i=0,j=0  0 < 3? T => i=0 j=0
		i++,j+=2 i=1,j=2 1 < 3? T => i=1 j=2
		i++,j+=2 i=2,j=4 2 < 3? T => i=2 j=4
		i++,j+=2 i=3,j=6 3 < 3? F => 跳出循环，结束
		输出结果：
		i=0 j=0
		i=1 j=2
		i=2 j=4
		*/
		for (int i = 0,j = 0; i < count; i++,j+=2) {
			System.out.println("i = " + i + " j = " + j);
		}
	}
}

image-20210711153808112

6.5、练习题

image-20210711162104639

**1: **

public class ForExercise01 {	public static void main(String[] args) {		//打印1~100之间所有是9的倍数的整数，统计个数及总和		//定义个数		int count = 0;		//定义总和		int sum = 0;		//先死后活编程思想		//1.为了适应更好的需求，把范围的开始的值和结束的值，做出变量		//2.9倍数也做成变量		int start = 1;	//开始的值		int end = 100;	//结束的值		int multiple = 9;	//倍数		for (int i = start; i <= end; i++) {			if (i % multiple == 0) {				System.out.print(i + " ");				count++;				sum+=i;			}		}		//换行		System.out.println("");		System.out.println("符合条件的一共有" + count + "个，总和为" + sum);	}}

image-20210711162217424

**2: **

public class ForExercise02 {	public static void main(String[] args) {		/* 执行流程		i=0,j=5 0 <= 5? T => 0 + 5 = 5		i++,j-- i=1,j=4 1 <= 5? T => 1 + 4 = 5		i++,j-- i=2,j=3 2 <= 5? T => 2 + 3 = 5		i++,j-- i=3,j=2 3 <= 5? T => 3 + 2 = 5		i++,j-- i=4,j=1 4 <= 5? T => 4 + 1 = 5		i++,j-- i=5,j=0 5 <= 5? T => 5 + 0 = 5		i++,j-- i=6,j=-1 6 <= 5? F => 跳出循环		*/		int start = 0;		int end = 5;		for (int i = start,j = end; i <= end; i++,j--) {			/*System.out.print(i + " + ");			System.out.print(j);			System.out.println(" = " + (i+j));*/			System.out.println(i + " + " + j + " = " + (i+j));		}	}}

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7、while循环控制

7.1、基本语法

image-20210711163445328

7.2、执行流程分析

image-20210711170030120

public class While01 {	public static void main(String[] args) {		//提高代码的灵活性		int start = 1;		int end = 10;		while (start <= end) {			System.out.println("Hello, Java " + start);			start++;	//循环变量迭代		}	}}

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7.3、注意事项和细节说明

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7.4、练习

image-20210711171716902

**1： **

public class WhileExercise01 {
	public static void main(String[] args) {
		int start = 1;
		int end = 100;

		while (start <= end) {
			if (start % 3 == 0) {
				System.out.print(start + " ");
			}
			start++;
		}
	}
}

image-20210711172000388

**2: **

public class WhileExercise02 {
	public static void main(String[] args) {
		int start = 40;
		int end = 200;

		while (start <= end) {
			if (start % 2 == 0) {
				System.out.print(start + " ");
			}
			start++;
		}
	}
}

image-20210711172157147

8、do..while循环控制

8.1、基本语法

image-20210711172427882

8.2、执行流程分析

image-20210711172753865

public class DoWhile01 {	public static void main(String[] args) {		int start = 1;		int end = 10;		do {			System.out.println("Hello, Java " + start);			start++;		} while (start <= end);	}}

image-20210711173540851

8.3、注意事项和细节说明

image-20210711223120533

**1: **

public class DoWhileExercise01 {	public static void main(String[] args) {		//打印1-100		int start = 1;		int end = 100;		do {			System.out.print(start + " ");			start++;			//十个换一行			if ( start % 10 == 0) {				System.out.println("");			}		} while (start <= end);	}}

image-20210711223218000

**2: **

public class DoWhileExercise02 {	public static void main(String[] args) {		int start = 1;		int end = 100;		int sum = 0;		do {			sum+=start;			start++;		} while (start <= end);		System.out.println("和为：" + sum);	}}

image-20210711223640522

**3: **

public class DoWhileExercise03 {	public static void main(String[] args) {		int start = 1;		int end = 200;		int firstDivisor = 5;	//第一个除数		int secondDivisor = 3;	//第二个除数		int count = 0;		do {			if (start % firstDivisor == 0 && start % secondDivisor != 0) {				count++;			}			start++;		} while (start <= end);		System.out.println("个数为：" + count); //27	}}

image-20210711230102985

**4: **

import java.util.Scanner;public class DoWhileExercise04 {	public static void main(String[] args) {		Scanner sc = new Scanner(System.in);		char yes = 'y';		char no = 'n';		char answer = ' ';	//初始化 		do {			System.out.println("还钱吗？(y/n)：");			answer = sc.next().charAt(0);			System.out.println("使出五连鞭");		} while (answer == no);	}}

image-20210711231037786

9、多重循环控制

9.1、介绍

image-20210711231159585

image-20210711231217045

9.2、执行步骤分析

image-20210711233322821

public class Multiple {	public static void main(String[] args) {		/*	双层for		i=0 0<2? T => j=0 0<3? T => i=0 j=0			      j++ j=1 1<3? T => i=0 j=1			      j++ j=2 2<3? T => i=0 j=2			      j++ j=3 3<3? F => 跳出内循环	    i++ i=1 1<2? T => j=0 0<3? T => i=1 j=0	    			  j++ j=1 1<3? T => i=1 j=1	    			  j++ j=2 2<3? T => i=1 j=2	    			  j++ j=3 3<3? F => 跳出内循环	    i++ i=2 2<2? F => 跳出外循环	    输出结果：	    i=0 j=0	    i=0 j=1	    i=0 j=2	    i=1 j=0	    i=1 j=1	    i=1 j=2		*/		for (int i = 0; i < 2; i++) {			for (int j = 0; j < 3; j++) {				System.out.println("i = " + i + " j = " + j);			}		}	}}

image-20210711233349336

9.3、应用实例

image-20210711233439428

1、2：

import java.util.Scanner;public class MulForExercise01 {	public static void main(String[] args) {		//统计3个班成绩情况，每个班有5名同学，求出各个班的平均分和所有班级的平均分		/*		思路分析：		1.先计算一个班，5个学生的成绩，使用for		创建 scanner 对象，接收用户输入 		*/		Scanner sc = new Scanner(System.in);		//定义三个班的总分		double totalScore = 0;		//三个班的及格人数		int totalPass = 0;        for (int i = 1; i <= 3; i++) {        	//定义班级的总分			double sum = 0;        	for (int j = 1; j <= 5; j++) {				System.out.println("请输入" + i + "班第" + j + "个学生的成绩");				double score = sc.nextDouble();				//判断是否及格				if (score >= 60) {					totalPass++;				}				sum+=score;			}			double average = sum / 5;			System.out.println(i + "班总分为：" + sum + ", " + i + "班的平均分为：" + average);			totalScore+=sum;        }		System.out.println("所有班级总分为：" + totalScore + ", 所有班的平均分为：" + (totalScore / 15));		System.out.println("所有班级的及格人数为：" + totalPass);	}}

image-20210712195923142

**3: **

import java.util.Scanner;public class MulForExercise02 {	public static void main(String[] args) {		for (int i = 1; i <= 9; i++) {			for (int j = 1; j <= i; j++) {				System.out.print(j + " * " + i + " = " + (i * j) + "\t");			}			//换行			System.out.println("");		}	}}

image-20210712200936441

9.4、经典的打印金字塔

image-20210712201120341

**1: **

import java.util.Scanner;public class Stars01 {	public static void main(String[] args) {		Scanner sc = new Scanner(System.in);		System.out.println("请输入层数(1~*)：");		int totalLevel = sc.nextInt();		for (int i = 1; i <= totalLevel; i++) {			for (int j = 1; j <= i; j++) {				System.out.print("*");			}			//换行			System.out.println("");		}	}}

image-20210712201901082

**2: **

import java.util.Scanner;public class Stars04 {	public static void main(String[] args) {		/* 打印整个金字塔		*		//第1层	有1个*	2*1-1	有5=(总层数-1)个空格	   ***		//第2层	有3个*	2*2-1	有4=(总层数-2)个空格	  *****		//第3层	有5个*	2*3-1	有3=(总层数-3)个空格	 *******	//第4层	有7个*	2*4-1	有2=(总层数-4)个空格	*********	//第5层	有9个*	2*5-1	有1=(总层数-5)个空格   ***********	//第6层	有11个*	2*6-1	有0=(总层数-6)个空格   		...		//第...层 有2*n-1		有(总层数 - 当前层数)个空格		*/		Scanner sc = new Scanner(System.in);		System.out.println("请输入层数(1~*)：");		int totalLevel = sc.nextInt();		for (int i = 1; i <= totalLevel; i++) {			//输出空格			for (int j = 1; j <= totalLevel - i; j++) {				System.out.print(" ");			}			//输出*			for (int k = 1; k <= (2 * i - 1); k++) {				System.out.print("*");			}			//换行			System.out.println("");		}	}}

image-20210712211612596

**3: **

import java.util.Scanner;public class Stars03 {	public static void main(String[] args) {		/*	打印空心金字塔		*		//第1层 有1个*		有3=(总层数-1)个空格		输出第1个*和第1=(2 * 1 - 1)个*	   * *		//第2层 有2个*		有2=(总层数-2)个空格		输出第1个*和第3=(2 * 2 - 1)个*	  *   *		//第3层 有2个*		有1=(总层数-3)个空格		输出第1个*和第5=(3 * 2 - 1)个*	 *******	//第4层 有7个*		有0=(总层数-4)个空格		最后一层全部输出	第一层和最后一层(当前层数*2-1)		(总层数-当前层数)个空格	输出第1个*和(当前层数 * 2 -1)个*		*/		Scanner sc = new Scanner(System.in);		System.out.println("请输入层数(1~*)：");		int totalLevel = sc.nextInt();		for (int i = 1; i <= totalLevel; i++) {			//输出空格			for (int j = 1; j <= totalLevel -i; j++) {				System.out.print(" ");			}			//输出*			for (int k = 1; k<= (2 * i - 1); k++) {				if (k == 1 || k == (2 * i - 1) || i== totalLevel) {					System.out.print("*");				} else {					System.out.print(" ");				}			}			System.out.println("");		}	}}

image-20210712214838993

**4: **

import java.util.Scanner;public class Stars05 {	public static void main(String[] args) {			/*	打印菱形			分成上下两部分	上有totalLevel层  下有(totalLevel - 1)层		*		//第1层 有1个*					有2个空格		   ***		//第2层 有3个*					有1个空格		  *****		//第3层 有5个* (2*当前层数-1)		有0个空格  	((总层数 + 1) / 2 - 当前层数)  中间层 (总层数 + 1) / 2	   ***		//第1层	有3个*					有1个空格	    *		//第2层	有1个*					有2个空格			*/		Scanner sc = new Scanner(System.in);		System.out.println("请输入层数(1~*)：");		int totalLevel = sc.nextInt();		//上半部分		//		for (int i = 1; i <= totalLevel; i++) {	//层数			for (int k = 1; k <= totalLevel - i; k++) {				System.out.print(" ");			}			for (int j = 1; j <= (2 * i - 1); j++) {				System.out.print("*");			}			System.out.println("");		}		for (int i = 1; i <= totalLevel -1; i++) {	//层数			for (int k = 1; k <= i; k++) {				System.out.print(" ");			}			//从下往上打印* 满足 2 * 当前层数 - 1			for (int j = 2 * totalLevel - 1; j >= 2 * i - 1 + 2; j--) {				System.out.print("*");			}			System.out.println(" ");		}	}}

image-20210713090705044

**5: **

import java.util.Scanner;public class Stars06 {	public static void main(String[] args) {			/*	打印空心菱形			分成上下两部分	上有totalLevel层  下有(totalLevel - 1)层		*		//第1层 有1个*		有2个空格	打印第一个和最后一个*	   * *		//第2层 有2个*		有1个空格		  *   *		//第3层 有2个* 		有0个空格  		   * *		//第1层	有2个*		有1个空格	    *		//第2层	有1个*		有2个空格			*/		Scanner sc = new Scanner(System.in);		System.out.println("请输入层数(1~*)：");		int totalLevel = sc.nextInt();		//上半部分		for (int i = 1; i <= totalLevel; i++) {	//层数			for (int k = 1; k <= totalLevel - i; k++) {				System.out.print(" ");			}			for (int j = 1; j <= (2 * i - 1); j++) {				if (j == 1 || j == (2 * i - 1)) {					System.out.print("*");				} else {					System.out.print(" ");				}			}			System.out.println("");		}		for (int i = 1; i <= totalLevel -1; i++) {	//层数			for (int k = 1; k <= i; k++) {				System.out.print(" ");			}			//从下往上打印* 满足 2 * 当前层数 - 1			for (int j = 2 * totalLevel - 1; j >= 2 * i - 1 + 2; j--) {				if (j == 2 * totalLevel - 1 || j == 2 * i - 1 + 2) {					System.out.print("*");				} else {					System.out.print(" ");				}			}			System.out.println(" ");		}	}}

image-20210713092158784

10、跳转控制语句-break

10.1、需求

image-20210713093359393

import java.lang.Math;public class Break01 {	public static void main(String[] args) {		int count = 0;		//死循环		while (true) {			int num = (int)(Math.random() * 100) + 1;			if (num != 97) {				count++;			} else {				break;			}		}		System.out.println("生成97用了" + count + "次");	}}

image-20210713114154076

10.2、基本介绍

image-20210713094207581

10.3、快速入门

image-20210713095205855

public class Break02 {	public static void main(String[] args) {		int start = 1;		int end = 10;		int condition = 3;	//跳出循环的条件		int count = 0;		//记录循环了多少次		for (int i = start; i <= end; i++) {			if (i == condition) {				break;			}			count++;			System.out.println("ok" + i);		}		System.out.println("循环了" + count + "次");	}}

image-20210713095249650

10.4、注意事项和细节说明

image-20210713101215045

public class BreakDetail {	public static void main(String[] args) {		/*	执行流程分析		j=0 j<4 ? T => i=0 i<10? T => i==2? F => i=0				   i++ i=1 1<10? T => 1==2? F => i=1				   i++ i=2 2<10? T => 2==2? T => break label1		跳出循环		预计输出结果：		i=0		i=1		*/		label1:			for (int j = 0; j < 4; j++) {				label2:					for (int i = 0; i < 10; i++) {						if (i == 2) {							break label1;						}						System.out.println("i = " + i);					}			}	}}

image-20210713101322839

10.5、练习

image-20210713111127242

**1: **

public class BreakExercise01 {	public static void main(String[] args) {		int sum = 0;		int n = 0;		for (int i = 1; i <= 100; i++) {			sum+=i;			if (sum > 20) {				n = i;				break;			}		}		System.out.println("sum =" + sum);		System.out.println("当前数为：" + n);	}}

image-20210713112630611

2:

import java.util.Scanner;public class BreakExercise02 {	public static void main(String[] args) {		Scanner sc = new Scanner(System.in);		int opportunity = 3;	//机会				for (int i = opportunity; i >= 1; i--) {			System.out.println("请输入用户名：");			String name = sc.next();			System.out.println("请输入密码：");			String pwd = sc.next();			if ("丁真".equals(name) && "666".equals(pwd)) {				System.out.println("登录成功");				break;			} else {				System.out.println("账号或者密码错误，你还有" + (i - 1) + "次机会");			}		}	}}

image-20210713113700999

11、跳转控制语句-continue

11.1、基本介绍

image-20210713114220544

image-20210713114607454

11.2、快速入门

image-20210713115243908

public class Continue01 {	public static void main(String[] args) {		/* 执行流程分析		i=1 i<=4? T => i++ i=2 2==2? T => continue		    2<=4? T => i++ i=3 3==2? F => i=3		    3<=4? T => i++ i=4 4==2? F => i=4		    4<=4? T => i++ i=5 5==2? F => i=5		    5<=4? F => 退出循环		输出结果：		i=3		i=4		i=5		*/		int i = 1;		while (i <= 4) {			i++;			if (i == 2) {				continue;			}			System.out.println("i = " + i);		}	}}

image-20210713115317264

11.3、细节分析和说明

image-20210713115850660

public class ContinueDetail {	public static void main(String[] args) {		/* 执行流程分析		j=0 j<4? T => i=0 i<10? T => 0==2? F => i=0		          i++ i=1 1<10? T => 1==2? F => i=1		          i++ i=2 2<10? T => 2==2? T => continue		          i++ i=3 3<10? T -> 3==2? F => i=3		          ...		j++ j=1 1<4? T =>...		...		输出结果：		i=0		i=1		i=2		i=3		i=4		i=5		i=6		i=7		i=8		i=9		...		当 continue label1时		输出结果：		i=0		i=1		i=0		i=1		i=0		i=1		i=0		i=1		*/		label1:			for (int j = 0; j < 4; j++) {				lable2:					for (int i = 0; i < 10; i++) {						if (i == 2) {							//continue;	// 等价于 lable2							//continue label1;							continue lable2;						}						System.out.println("i = " + i);					}			}	}}

当 continue label1时:

image-20210713121610929

当 continue label 或者 continue labe2 时:

image-20210713121704021

12、跳转控制语句-return

12.1、介绍

image-20210713122303960

public class Return01 {	public static void main(String[] args) {		/*	执行流程分析		i=1 1<=5? T => 1==3? F => Hello Java!		i++ i=2 2<=5? T => 2==3? F => Hello Java!		i++ i=3 3<=5? T => 3==3? T => Java 天下第一3 => return 跳出方法		输出结果：		Hello Java!		Hello Java!		Java 天下第一3		为 contine 时：		Hello Java!		Hello Java!		Java 天下第一3		Hello Java!		Hello Java!		go on...		为 break 时：		Hello Java!		Hello Java!		Java 天下第一3		go on...		*/		for (int i = 1; i <= 5; i++) {			if (i == 3) {				System.out.println("Java 天下第一" + i);				return;				//continue;				//break;			}			System.out.println("Hello Java!");		}		System.out.println("go on...");	}}

为 return 时

image-20210713124056969

为 continue 时

image-20210713124246585

为 break 时

image-20210713124326673

13、作业

image-20210713124953623

**1: **

public class Homework01 {	public static void main(String[] args) {		double money = 100000;		//定义次数		int count = 0;		while (true) {			if (money > 50000) {				money = money - (money * 0.05);				count++;			} else if (money >= 1000) {				money = money - 1000;				count++;			} else if (money < 1000) {				break;			} else {				System.out.println("输入错误，请重新输入");			}		}		System.out.println("剩余" + money + "元, 不足以通行");		System.out.println("可以经过" + count + "个路口");	}}

image-20210713135854054

**2: **

import java.util.Scanner;public class Homework02 {	public static void main(String[] args) {		Scanner sc = new Scanner(System.in);		System.out.println("请输入一个整数：");		int num = sc.nextInt();		if (num > 0) {			System.out.println(num + "大于0");		} else if (num == 0) {			System.out.println(num + "等于0");		} else {			System.out.println(num + "小于0");		}	}}

image-20210713142629157

**3: **

import java.util.Scanner;public class Homework03 {	public static void main(String[] args) {		Scanner sc = new Scanner(System.in);		System.out.println("请输入一个年份：");		int year = sc.nextInt();		if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0)) {			System.out.println(year + "是闰年");		} else {			System.out.println(year + "不是闰年");		}	}}

image-20210713142721736

**4: **

import java.util.Scanner;public class Homework04 {	public static void main(String[] args) {		Scanner sc = new Scanner(System.in);		System.out.println("请输入一个三位数：");		int num = sc.nextInt();		//个位		int ge = num % 10;		//十位		int shi = num % 100 / 10;		//百位		int bai = num / 100;		if (num == ((ge * ge * ge) + (shi * shi * shi) + (bai * bai * bai))) {			System.out.println(num + "是水仙花数");		} else {			System.out.println(num + "不是水仙花数");		}	}}

image-20210713143358273

image-20210713143846147

public class Homework05 {	public static void main(String[] args) {		/* 执行流程分析		m=0 n=3 0>0? F =>		*/		int m = 0;		int n = 3;		if (m > 0) {			if (n > 2) {				System.out.println("ok1");			} else {				System.out.println("ok2");			}		}	}}

image-20210713143914023

没有任何输出

image-20210713151141722

**6: **

public class Homework06 {	public static void main(String[] args) {		//定义个数		int count = 0;		for (int i = 1; i <= 100; i++) {			if (i % 5 != 0) {				count++;				System.out.print(i + "\t");			}			//每满5个就换行			if (count % 5 == 0) {				System.out.println("");			}		}	}}

image-20210713151227131

**7: **

public class Homework07 {	public static void main(String[] args) {		char c1 = 'a';		char c2 = 'z';		char c3 = 'Z';		char c4 = 'A';		for (int i = c1; i <= c2; i++) {			System.out.print((char)i + " ");		}		System.out.println("");				for (int i = c3; i >= c4; i--) {			System.out.print((char)i + " ");		}	}}

image-20210713151707948

**8: **

public class Homework08 {	public static void main(String[] args) {		double sum = 0;		for (int i = 1; i <= 100; i++) {			//如果是奇数			if (i % 2 != 0) {				sum+=(1.0/i);			} else {				sum-=(1.0/i);			}		}		System.out.println("和为：" + sum);	}}

image-20210713152745211

**9: **

public class Homework09 {	public static void main(String[] args) {		int sum = 0;		for (int i = 1; i <= 100; i++) {			for (int j = 1; j <= i; j++) {				sum+=j;			}		}		System.out.println("和为：" + sum);	}}

image-20210713153324950

14、两个编程思想

  1. 化繁为简：将复杂的需求，拆解成简单的需求，逐步完成
  2. 先死后活：先考虑固定的值，然后转成可以灵活变化的值
posted @ 2021-08-24 23:27  多瑞C  阅读(140)  评论(0)    收藏  举报