Day04
Scanner对象
基本语法:
Scanner s = new Scanner(System.in);
next(),nextLine() 来获取字符串
package scanner; import java.util.Scanner; public class Demo01 { public static void main(String[] args) {
选择结构
if单选结构
if(布尔表达式){ true; } false;
//equals 判断字符串是否相等
if双选结构
if(布尔表达式){ true; } else { false; }
if多选结构
if(布尔表达式1){ 布尔表达式1为true; } else if(布尔表达式2){ 布尔表达式2为true; } else if(布尔表达式3){ 布尔表达式3为true; } else { 以上布尔表达式都不为true; }
if嵌套结构
switch多选结构
switch(expression){ case value;
循环结构
while循环(先判断,后执行)
while (布尔表达式){
public class WhileDemo01 { public static void main(String[] args) {
do...while循环(先执行,后判断)
public class DoWhileDemo01 { public static void main(String[] args) {
do...while总是保证循环体会至少执行一次(这是与while的主要差别)
for循环(重中之重)
for(初始化;布尔表达式;迭代){
练习题
练习1
public class Test01 { public static void main(String[] args) { int sum0 = 0; int sum1 = 0; for (int i = 0; i <= 100; i += 2) { sum0 = sum0 + i; } System.out.println("sum0=" + sum0); for (int j = 1; j <= 100; j += 2) { sum1 = sum1 + j; } System.out.println("sum1=" + sum1); System.out.println("========================="); sum0 =0; sum1 =0; for (int k = 0; k <= 100; k ++) { if(k%2==0){ sum0 = sum0 + k; } else{ sum1 = sum1 + k; } }System.out.println("sum1=" + sum1+"sum0="+sum0); } }
练习2
public class Test02 { public static void main(String[] args) { for (int i = 1; i <= 1000; i++) { if(i%5==0){ System.out.print(i+"\t"); } if(i%(5*3)==0){ System.out.print("\n"); } } } }
9*9乘法表
public class Test03 { 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"); } System.out.println(); } } }
增强for循环(循环数组和集合的)
public class ForDemo01 { public static void main(String[] args) { int[] numbers = {10,20,30,40,50};
打印三角形
public class Test04 { public static void main(String[] args) { for (int i = 1; i <= 5; i++) { for (int j = 5; j >= i; j--){ System.out.print(" "); } for (int j = 1; j <= i; j++){ System.out.print("*"); } for (int j = 1; j < i; j++){ System.out.print("*"); } System.out.println(); } } }
倒三角
public class Test05 { public static void main(String[] args) { for (int i = 1; i <= 5; i++) { for (int j = 1; j <= i; j++){ System.out.print(" "); } for (int x = 1; x <= 9-2*(i-1); x++){ System.out.print("*"); } System.out.println(); } } }
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