Java Programming Fundamentals stage notes day04 Java basic grammar (lower)

day04 Java basic grammar (lower)

Important notes Notes

Note switch-case statement
Title switch-case (switchTest5)
Cycle execution order
if-else an integer of 3 to achieve sorting
String string comparison
Cycle four elements
Print multiplication table
Special keyword continue, break

switch (expression) expression in only supports byte, short, char, int, enum, String (after jdk1.7)

switch (expression) {

Constant case 1:

Statement 1 is executed;

break;

Constant case 2:

Execute the statement 2;

break;

......

default:

Execute the statement n;

break;

}

Behind the case only with constants, default is optional. If you do not match the successful implementation of the statement is executed in default. The default position is flexible.
switch-case, and can be replaced if-else, some of the high switch-case efficiency

Enter the year, respectively, from the keyboard, month, day, judgment day is the day of the year

Note: to determine whether a year is a leap year criteria:

1) is divisible by four, but not divisible by 100

2) 400 may be divisible

import java.util.Scanner;

public class SwitchTest5{

public static void main(String[] args){

1 // Read data

Scanner sc = new Scanner(System.in);

System.out.println ( "Please enter the year");

int year = sc.nextInt();

System.out.println ( "Please enter the month");

int month = sc.nextInt();

System.out.println("请输入日期");

int day = sc.nextInt();

int sumDay = 0; //用来统计当年的总天数

//2.统计天数

switch(month){

case 4:

sumDay += 31;

case 3:

//判断当年是否是闰年

if((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)){

sumDay += 29;

}else{

sumDay += 28;

}

case 2:

sumDay += 31;

case 1:

sumDay += day;

}

//3.输出

System.out.println(year + "年" + month + "月" + day + "日是当年的第" + sumDay + "天");

}

编写程序：由键盘输入三个整数分别存入变量num1、num2、num3，

对它们进行排序(使用 if-else if-else),并且从小到大输出。

import java.util.Scanner;

public class IfTest

{

public static void main(String[] args){

Scanner sc = new Scanner(System.in);

System.out.println("请输入三个数字");

int num1,num2,num3;

num1 = sc.nextInt();

num2 = sc.nextInt();

num3 = sc.nextInt();

if(num1>num2){

if(num3>num1){//num3最大

System.out.println("小到大："+ num2 +" "+ num1 +" "+ num3);

}else if(num3<num2){//num3最小

System.out.print("小到大："+ num3 + " " + num2 + " " + num1);

}else{

System.out.println("小到大："+ num2 + " " + num3 + " " + num1);

}

}else{//num1<num2

if(num3>num2){//num3最大

System.out.println("小到大："+ num1 + " "+ num2 + " "+ num3);

}else if(num3<num1){//num2最大

System.out.println("小到大："+ num3 + " " + num1 + " " + num2);

}else{

System.out.println("小到大："+ num1 + " " + num3 + " " + num2);

}

String字符串比较

String str = new String("帅");

//判断帅不帅

System.out.println("帅" == str); //这样不能比字符串的内容

boolean handsome = "帅".equals(str); //比较的是字符串的内容 - 如果内容相同返回true否则返回false

switch使用小技巧

对学生成绩大于60分的，输出“合格”。低于60分的，输出“不合格”

switch(score / 60){

case 0:

System.out.println("不合格");

break;

case 1:

System.out.println("合格");

break;

编写程序：输入月，日，输出第几天

4. 编写程序：从键盘上输入2019年的“month”和“day”，要求通过程序输出输入的日期为2019年的第几天。

import java.util.Scanner;

public class SwitchTest4{

public static void main(String[] args){

//1.读取数据

Scanner sc = new Scanner(System.in);

System.out.println("请输入月份");

int month = sc.nextInt();

System.out.println("请输入日期");

int day = sc.nextInt();

int sumDay = 0; //用来统计当年的总天数

//2.统计天数

switch(month){

case 1:

sumDay = day;

break;

case 2:

sumDay = day + 31;

break;

case 3:

sumDay = day + 31 + 28;

break;

case 4:

sumDay = day + 31 + 28 + 31;

break;

case 4:

sumDay += 31;

case 3:

sumDay += 28; //赋值和+=完全不一样。sumDay += 28 : 除了sumDay原来的天数再额外加上28

case 2:

sumDay += 31; // sumDay = sumDay + 31

case 1:

sumDay += day;

}

//3.输出

System.out.println("2019年" + month + "月" + day + "日是当年的第" + sumDay + "天");

}

编写程序：输入年，月，日，输出第几天

从键盘分别输入年、月、日，判断这一天是当年的第几天

注：判断一年是否是闰年的标准：

1）可以被4整除，但不可被100整除

或

2）可以被400整除

import java.util.Scanner;

public class SwitchTest4

{

public static void main(String[] args){

Scanner sc = new Scanner(System.in);

System.out.println("请输入年份：");

int year = sc.nextInt();

System.out.println("请输入月份：");

int month = sc.nextInt();

System.out.println("请输入天数：");

int day = sc.nextInt();

int sumDay = 0;

switch(month){

case 12:

sumDay += 30;

case 11:

sumDay += 31;

case 10:

sumDay += 30;

case 9:

sumDay += 31;

case 8:

sumDay += 31;

case 7:

sumDay += 30;

case 6:

sumDay += 31;

case 5:

sumDay += 30;

case 4:

sumDay += 31;

case 3:

// 28或 29

if((year%4==0&&year%100!=0)||year % 400 ==0){//闰年

sumDay += 29;

}else{

sumDay += 28;

}

case 2:

sumDay += 31;

case 1:

sumDay += day;

break;

}

System.out.println(year+"年" + month + "月" + day + "日是当年的第" + sumDay + "天");

}

循环四要素

循环的四个部分：

1.初始化条件

2.循环条件

3.循环体

4.迭代条件

打印九九乘法表

1*1=1

1*2=2 2*2=4

1*3=3 2*3=6 3*3=9

打印九九乘法表

public class c99

{

public static void main(String[] args){

int i,j;

for(i=1;i<=9;i++){//9行

for(j=1;j<=i;j++){

System.out.print(j + "*" +i+" = "+ i*j +" ");

}

System.out.println();

}

特殊关键字continue、break

break用于 switch-case语句与循环结构中，表示结束当前case语句，结束循环语句
continue，用于循环结构表示结束当此循环。
在嵌套循环中break结束的包含该语句的循环语句，对外层循环无作用
在嵌套循环中continue跳出的是包含他的循环语句的当次循环，不跳出

嵌套循环中如何使用内部循环的break结束外层循环

可以给循环命名，break + 循环名字

总结Summary

if-else实现三个整数排序
打印九九乘法表
break，continue使用注意事项

Java Programming Fundamentals stage notes day04 Java basic grammar (lower)

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