java流程控制(重点)

java流程控制

目录

• java流程控制
  • 结构有
    • • • 顺序结构
        • 选择结构
        • 循环结构
    • 选择结构
      • if
      • if else
      • if ,else if,
      • switch,break,default
      • String
    • 循环结构
      • while
      • do while
      • for循环
        • 1.基础语法
        • 2.练习1
        • 3.练习2
        • 4.练习3
    • Break及Continue
      • 1.基础
      • 2.Break
      • 3.Continue
    • 练习及Debug
      • 1.练习
      • 2.Debug

结构有

1. 顺序结构

2. 选择结构

3. 循环结构

选择结构

if

package struct;
import java.util.Scanner;

public class dome1 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入内容");
        String s = scanner.nextLine();
        //equals:判断字符串是否相等
        if (s.equals("hello")){
            System.out.println(s);
        }
        System.out.println("end");
        scanner.close();

    }
}

if else

package struct;

import java.util.Scanner;

public class dome2 {
    public static void main(String[] args) {
        //考试分数大于60及格,小于60不及格
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入成绩:");
        int score = scanner.nextInt();
        if (score >= 60) {
            System.out.println("及格");
        } else {
            System.out.println("不及格");
        }
        scanner.close();
    }
}

if ,else if,

package struct;

import java.util.Scanner;

public class dome3 {

    public static void main(String[] args) {

        /**
         * if 语句至少有一个else语句,else语句在所有else if 之后
         * 一旦其中有一个else if 语句为true ,其他else if及else语句都将跳过执行
         */

        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入成绩:");
        int score = scanner.nextInt();
        if (score==100){
            System.out.println("满分");
        }else if (score<100 && score>=90){
            System.out.println("A");
        }else if (score<90 && score>=80){
            System.out.println("B");
        }else if (score<80 && score>=70){
            System.out.println("C");
        }else if (score<70 && score>=60){
            System.out.println("D");
        }else if (score<60 && score>=0){
            System.out.println("不及格");
        }else {
            System.out.println("成绩不合法");
        }
        scanner.close();
    }


}

switch,break,default

package struct;

public class dome4 {
    public static void main(String[] args) {
        //case穿透 //switch匹配一个具体值

        char grade = 'A';
        switch (grade) {
            case 'A':
                System.out.println("优秀");
                break;
            case 'b':
                System.out.println("良");
                break;
            case 'c':
                System.out.println("及格");
                break;
            case 'd':
                System.out.println("不及格");
                break;
            default:
                System.out.println("未知");
        }
    }

}

String

循环结构

while

package struct;

public class dome6 {
    public static void main(String[] args) {
        //输出1~100
        int i = 0;
        while (i < 100) {
            i++;
            System.out.println(i);
        }

    }
}

package struct;

public class whlieDome {
    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("100以内和为;"+sum);//5050

    }
}

do while

package struct;

public class dowhlie {
    public static void main(String[] args) {
        int i = 0;
        int sum = 0;
        do {
            sum = sum + i;
            i++;

        } while (i <= 100);
        System.out.println(sum);

    }
}

for循环

1.基础语法

package struct;

public class fordome {
    public static void main(String[] args) {
        int a = 1;//初始化条件
        while (a<=100){//条件
            System.out.println(a);//循环体
            a+=2;//迭代
        }
        System.out.println("while循环结束");
        //初始化 //条件 //迭代
        for (int i = 1; i <= 100; i = i+2) {
            System.out.println(i);

        }
        System.out.println("for循环结束");
    }
}

2.练习1

package struct;public class fordome1 {    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("奇数和:"+oddSum);//2500        System.out.println("偶数和:"+evenSum);//2550    }}

3.练习2

package struct;public class fordome2 {    public static void main(String[] args) {        //for循环输出1-1000之间能被5整除的,并且每行输出3个        for (int i = 0; i <= 1000; i++) {            if (i%5==0){                System.out.print(i+"\t");            }            if (i%(5*3)==0){//每行3个                System.out.println();                //System.out.print("\n");                //println 输出完换行                //print 输出完不换行            }        }    }}

4.练习3

package struct;public class fordome3 {    public static void main(String[] args) {        //99乘法表        //打印第一列        //把固定的1再用循环包起来        //去掉重复值 i<=j        //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();        }    }}

Break及Continue

1.基础

2.Break

package struct;public class BreakDome {    public static void main(String[] args) {        for (int i = 1; i < 100; i++) {            System.out.println(i);            if (i==30){                break;            }        }        System.out.println("结束");    }}

3.Continue

package struct;public class ContinueDome {    public static void main(String[] args) {        for (int i = 0; i < 100; i++) {            if (i % 10 == 0) {                System.out.println();                continue;            }            System.out.print(i);        }    }}

练习及Debug

1.练习

package struct;public class Exercise {    public static void main(String[] args) {        //打印三角形 5        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();        }    }}     *    ***   *****  ******* *********

2.Debug