流程控制

Scanner对象

next()和nextLine()方法

顺序结构

选择结构

单选择结构

双选择结构

多选择结构

嵌套

switch多选择结构

break：防止case穿透

了解IDEA反编码

package struct;

import java.util.Scanner;

public class SwitchSelect {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入");
        String score = scanner.next();
        switch (score){
            case "a":
                System.out.println("a");
                break;
            case "b":
                System.out.println("b");
                break;
            case "c":
                System.out.println("c");
                break;
            default:
                System.out.println("错误");
        }
scanner.close();
    }
}

循环结构

while循环

public class WhileCycle {
    public static void main(String[] args) {
        //计算1-100的和
        int i = 0;
        int total = 0;
        while(i<100){
            i++;
            total += i;
        }
        System.out.println("总和是："+total);
    }
}

do-while循环

public class DoWhileCycle {
    public static void main(String[] args) {
        //计算1-100的和
        int i = 0;
        int total = 0;
        do {
            i++;
            total += i;
        }while (i<100);
        System.out.println("总和是："+ total);
    }
}

for循环

public class ForCycle {
    //计算1-100的和
    public static void main(String[] args) {
        int total = 0;
        for(int i=0; i <= 100; i++){
            total += i;
        }
        System.out.println("和是："+ total);
    }
}

//test1
public class CycleTest01 {
    public static void main(String[] args) {
        //0-100奇数的和
        int sum1 = 0;
        for(int i = 1; i <= 100; i+=2){
            sum1 += i;
        }
        System.out.println("奇数的和为："+sum1);
        //0-100偶数的和
        int sum2 = 0;
        for(int a = 2; a <= 100; a+=2){
            sum2 += a;
        }
        System.out.println("偶数的和为："+sum2);
        //方法二
        int oddSum = 0;
        int evenSum = 0;
        for (int i = 0; i <= 100; i++) {
            if(i % 2 == 0){
                evenSum += i;
            }else {
                oddSum += i;
            }

        }
        System.out.println("奇数和为"+ oddSum +"偶数和为"+ evenSum);
    }
}

//test2 1-1000之间能被5整除的数，每行输出3个
public class CycleTest02 {
    //1-1000之间能被5整除的数，每行输出3个
    public static void main(String[] args) {
        for (int i = 1; i <= 1000; i++) {
            if(i%5 == 0){
                System.out.print(i + "\t");
            }
            if (i%15 == 0){
                System.out.println();
            }
        }
    }
}

//test3 九九乘法表
public class CycleTest03 {
    public static void main(String[] args) {
        //九九乘法表
        for (int i = 1; i <= 9; i++) {
            for (int j = 1; j <= i; j++) {
                System.out.print(i+"*"+j+"="+(i*j)+"\t");
            }
            System.out.println();
        }
    }
}

增强for循环

break、continue

public class GotoLable {
    public static void main(String[] args) {
        //101-150的质数
        int count = 1;
        //了解，尽量不使用
        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+"\t");

        }
    }
}

practice

public class CycleTest04 {
    public static void main(String[] args) {
        //打印三角形
        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();
        }
    }
}