switch多选择结构
- switch case语句判断一个变量与一系列值中某个值是否相等，每个值称为一个分支
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package com.struct;public class Swicth01 {public static void main(String[] args) {//case穿透//switch匹配一个具体的值char grade = 'B';switch (grade){case 'A':System.out.println("优秀");break;//可选case 'B' :System.out.println("良好");break;//可选case 'C' :System.out.println("及格");break;//可选case 'D' :System.out.println("再接再厉");break;//可选case 'E' :System.out.println("挂科");break;//可选default:System.out.println("未知等级");}}
}
package com.struct;public class Swicth02 {public static void main(String[] args) {String name = "琴江";//JDK7新特性，表达式结果可以是字符串//字符的本质是数字//反编译 java---class(字节码文件)----反编译（IDEA）switch (name){case "琴江":System.out.println("琴江");break;case "狂神":System.out.println("狂神");break;default:System.out.println("弄啥嘞！");}}
}
循环结构
1.while循环
输出0~100
package com.struct;public class While01 {public static void main(String[] args) {//输出0~100int i = 0;while (i<100){i++;System.out.println(i);}}
}
死循环
package com.struct;public class While02 {public static void main(String[] args) {//死循环while (true){//等待客户端连接//定时检查//。。。。。。。}}
}
计算1+2+3+...+100=?
package com.struct;public class While03 {public static void main(String[] args) {//计算1+2+3+...+100=?int i=0;int sum = 0;while (i<=100){sum = sum + i;i++;}System.out.println(sum);}
}
2.do...while循环
package com.struct;public class DoWhile01 {public static void main(String[] args) {int i =0;int sum = 0;do {sum = sum + i;i++;}while (i<=100);System.out.println(sum);}
}
while和do...while的区别
package com.struct;public class DoWhile02 {public static void main(String[] args) {int a = 0;while (a<0){System.out.println(a);a++;}System.out.println("==========");do {System.out.println(a);a++;}while (a<0);}
}
3.for循环
package com.struct;public class For01 {public static void main(String[] args) {int a = 1;//初始化条件while (a<=100) {//条件判断System.out.println(a);a+=2;//迭代}System.out.println("while循环结束！");//初始化+布尔表达式+更新for (int i=1;i<=100;i++){System.out.println(i);}System.out.println("for循环结束");//死循环for (; ; ) {}}
}
练习1：
package com.struct;public class For02 {public static void main(String[] args) {int oddSum = 0;int evenSum = 0;for (int i = 0; i < 100; i++) {if (i%2!=0){oddSum+=i;}else {evenSum+=i;}}System.out.println("奇数的和"+oddSum);System.out.println("偶数的和"+evenSum);}
}
练习2：
package com.struct;public class For03 {public static void main(String[] args) {for (int i = 0; i <= 1000; i++) {if (i%5==0){System.out.println(i+"\t");}if (1%(5*3)==0){System.out.println();//换行//System.out.print("\n");换行}}//println 输出完会换行//print 输出完不会换行}
}
练习3：
package com.struct;public class For04 {public static void main(String[] args) {//1.先打印第一列//2.把固定的1再用一个循环包起来//3.去掉重复项 i <= j//4.调整样式for (int j = 1; j <= 9; j++) {for (int i = 1; i <= j; i++) {System.out.print(j+"*"+i+"="+(j*i) + "\t");}System.out.println();}}
}
4.增强for循环
package com.struct;public class For05 {public static void main(String[] args) {int[] numbers = {10,20,30,40,50,};//定义了一个数组for (int i = 0; i<5;i++){System.out.println(numbers[i]);}System.out.println("========");//遍历数组的元素for (int x:numbers){System.out.println(x);}}
}
5.break continue goto
break
package com.struct;public class Break01 {public static void main(String[] args) {int i = 0;while (i<100){i++;System.out.println(i);if (i==30){break;}}System.out.println("123");}
}
continue
package com.struct;public class Continue01 {public static void main(String[] args) {int i = 0;while (i<100){i++;if(i%10==0){System.out.println();continue;}System.out.print(i);}}
}
goto (lable标签）
package com.struct;public class Label01 {public static void main(String[] args) {//打印101~150之间所有的质数//质数是指再大于1的自然数中，出了1和它本身意外不再有其他因数的自然数。int count = 0;//不建议使用outer:for (int i=101;i<150;i++){for (int j=2;j<i/2;j++){if (i%j==0){continue outer;}}System.out.print(i+" ");}}
}
流程控制练习
- 打印三角形
package com.struct;public class Test01 {public static void main(String[] args) {//打印三角形 5行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();}}
}