目录

前言

一、基本结构

1.if语句

 2.switch case语句

二、选择语句应用实例

1.判断闰年

2.判断奇偶数

3.小型计算机系统

总结


前言


        选择结构用于判断给定的条件,根据判断的结果判断某些条件,根据判断的结果来控制程序的流程。今天,让我们一起学习if和switch两种选择语句及实例吧!


一、基本结构

1.if语句

(1)if(表达式){
            语句一
         }

public void test() {
	Scanner sc = new Scanner(System.in);
	System.out.println("请输入a:");
	String a  = sc.nextLine();
		
	char s  = a.charAt(0);//取出字符串的第一个字母
	if(s<='0' && s>='9') {
		System.out.println(s+"是数字");
	}if(s>='A' && s<='Z') {
		System.out.println(s+"是大写字母");
	}if(s>='a' && s<='z') {
		System.out.println(s+"是小写字母");
	}if(s>='\u4e00' && s<='\u9fa5') { //utf-8的中文编码范围
		System.out.println(s+"是中文");
	}
}

javafx mulu选择器 java的选择语句_Math

 (2)  if(表达式1){
            语句一
        }else if(表达式2){
            语句二
        }else{
            语句三
        }

public void test1() {
	Scanner sc = new Scanner(System.in);
	System.out.println("请输入a:");
	String a  = sc.nextLine();
		
	if(a.equals(" ")|| a == null) {
		System.out.println("输入为空...");
		return ; //返回,结束程序
	}
		
	char s  = a.charAt(0);//取出字符串的第一个字母
	if(s<='0' && s>='9') {
		System.out.println(s+"是数字");
	}else if(s>='A' && s<='Z') {
		System.out.println(s+"是大写字母");
	}else if(s>='a' && s<='z') {
		System.out.println(s+"是小写字母");
	}else if(s>='\u4e00' && s<='\u9fa5') { //utf-8的中文编码范围
		System.out.println(s+"是中文");
	}else {
		System.out.println(s+"是其他字符");
	}
}

javafx mulu选择器 java的选择语句_javafx mulu选择器_02

javafx mulu选择器 java的选择语句_Math_03

 2.switch case语句

switch(表达式){
        case 1:
                break;
        case2:
                break;
        ....
        default:
                break;
}
public void test2() {
	Scanner sc = new Scanner(System.in);
	System.out.println("请输入(周一~周天):");
	String s = sc.nextLine();
		
	switch(s) {
	case "周一":
		System.out.println("开例会!");
		break;
	case "周二":
		System.out.println("项目分析!");
		break;
	case "周三":
		System.out.println("项目开发!");
	    break;
	case "周四":
		System.out.println("项目测试!");
		break;
	case "周五":
		System.out.println("项目验收!");
		break;
	case "周六"://越界(周六周天干同一件事)
	case "周天":
		System.out.println("休息!");
		break;
	default:
		System.out.println("输入不合法...");
		break;
	}
}

javafx mulu选择器 java的选择语句_字符串_04

二、选择语句应用实例

1.判断闰年

public void isLeap() {
	Scanner sc = new Scanner(System.in);
	System.out.println("请输入年份:");
	int year = Integer.parseInt(sc.nextLine());
		
	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");
	}
}

 2.判断奇偶数

public void EvenTest() {
	Scanner sc = new Scanner(System.in);
	System.out.println("请输入数字a:");
	int a = Integer.parseInt(sc.nextLine());
		
	if(a%2==0) {
		System.out.println(a+"是偶数");
	}else {
		System.out.println(a+"是奇数");
	}
}

3.小型计算机系统

public void demo1() {
	Scanner  sc = new Scanner(System.in);
		
	final String PLUS = "1";
	final String SUB = "2";
	final String MUL = "3";
	final String DIVI = "4";
	final String POW = "5";
	final String MOD = "6";
	final String SQRT = "7";
	final String EVEN = "8";
	final String MAX = "9";
	final String SORT_MAX_TO_MIN = "10";
	final String EXIT = "0";
	final int EVEN_FLAG = 2;
	
	int a = 0,b = 0;
	double x = 0,y =0 ;
		
		
	System.out.println("-------------------------------");
	System.out.println("1.加法\t     2.减    法\t  ");
	System.out.println("3.乘法\t     4.除    法\t  ");
	System.out.println("5.幂     \t     6.取模\t  ");
	System.out.println("7.开    方\t    8.是否为偶数\t  ");
	System.out.println("9.最大值\t    10.从大至小排序\t  ");
	System.out.println("0.退出");
	System.out.println("-------------------------------");
		
	System.out.println("请选择运算方式");
	String choice = sc.nextLine();
		
	switch (choice) {
	case EXIT:
		char s = choice.charAt(0);//取出字符串的第一个字母
		if(s == 0) {
		System.out.println("已退出");
		//return ;
		}
		break;
	case PLUS:
		System.out.println("请输入数字a:");
		a = Integer.parseInt(sc.nextLine());
		System.out.println("请输入数字b:");
		b = Integer.parseInt(sc.nextLine());
		int sum = a+b;
		System.out.println(a+"+"+b+"="+ sum);
		break;
	case SUB:
		System.out.println("请输入数字a:");
		a = Integer.parseInt(sc.nextLine());
		System.out.println("请输入数字b:");
		b = Integer.parseInt(sc.nextLine());
		int sub = a-b;
		System.out.println(a+"-"+b+"="+ sub);
		break;
	case MUL:
		System.out.println("请输入数字am:");
		a = Integer.parseInt(sc.nextLine());
		System.out.println("请输入数字b:");
		b = Integer.parseInt(sc.nextLine());
		int mul = a*b;
		System.out.println(a+"*"+b+"="+ mul);
		break;
	case DIVI:
		System.out.println("请输入除数x:");
		x = Double.parseDouble(sc.nextLine());
		System.out.println("请输入被除数y:");
		y = Double.parseDouble(sc.nextLine());
		if(y != 0) {
			double d = x / y;
			System.out.println(x+"➗"+y+"="+ d);
		}else {
			System.out.println("被除数不能为0");
		}
		break;
	case POW:
		System.out.println("请输入数字x:");
		x = Double.parseDouble(sc.nextLine());
		System.out.println("请输入数字y:");
		y = Double.parseDouble(sc.nextLine());
		int result = (int)Math.pow(x, y);
		System.out.println(x+"^"+y+"="+result);
		break;
	case MOD:
		System.out.println("请输入数字x:");
		x = Double.parseDouble(sc.nextLine());
		System.out.println("请输入数字y:");
		y = Double.parseDouble(sc.nextLine());
		double result1 = x%y;
		System.out.println(x+"%"+y+"="+result1);
		break;
	case SQRT:
		System.out.println("请输入数字x:");
		x = Double.parseDouble(sc.nextLine());
		double result2 = Math.sqrt(x);
		System.out.println(x+"开方的结果:"+result2);
		break;
	case EVEN:
		System.out.println("请输入数字a:");
		a = Integer.parseInt(sc.nextLine());
		if(a%EVEN_FLAG == 0) {
			System.out.println(a+"是偶数");
		}else {
			System.out.println(a+"不是偶数");
		}
		break;
	case MAX:
		System.out.println("请输入数字a:");
		a = Integer.parseInt(sc.nextLine());
		System.out.println("请输入数字b:");
		b = Integer.parseInt(sc.nextLine());
		//int max = Math.max(a, b);
		System.out.println(a+"和"+b+"之间的最大值为:"+Math.max(a, b));
		break;
	case SORT_MAX_TO_MIN:
		System.out.println("请输入数字a:");
		a = Integer.parseInt(sc.nextLine());
		System.out.println("请输入数字b:");
		b = Integer.parseInt(sc.nextLine());
		int max = Math.max(a, b);
		int min = Math.min(a, b);
		System.out.println("由大到小排序为:"+max+" ,"+min);
		break;
	default:
		System.out.println("输入不合法!");
		break;
	}
}

运行结果部分截图:

 

javafx mulu选择器 java的选择语句_System_05

javafx mulu选择器 java的选择语句_字符串_06


总结

        本文对if和switch两种选择进行基本结构和实例应用的介绍,希望大家在遇到分支型问题时能对选择结构加以应用。本人才疏学浅,有问题请大家多多指教!