Java顺序结构及if选择结构

• Java的基本结构为顺序结构，除非特别指名，否则就按照顺序一句一句执行。
• 顺序结构是最简单的算法结构
• 语句与语句之间，框与框之间按照从上到下的顺序进行的，是由若干个依次执行的处理步骤组成的，他是任何一个算法都离不开的一种基本算法结构

package struct;



public class Demo01 {
    public static void main(String[] args) {
        System.out.println(1);
        System.out.println(2);
        System.out.println(3);
        System.out.println(4);
        System.out.println(5);
    }
}

package struct;

import java.util.Scanner;



public class Demo02 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入内容：");
        String s = scanner.nextLine();
        if (s.equals("Hello")) {  //equals:判断字符串是否相等，少用==
            System.out.println(s);
        }
        System.out.println("End");


        scanner.close();
    }
}

package struct;

import java.util.Scanner;



public class Demo03 {
    public static void main(String[] args) {
        //考试大于60分及格，否则不及格
        System.out.print("grade=");
        Scanner scanner = new Scanner(System.in);
        Double grade = scanner.nextDouble();
        if (grade > 60){
            System.out.println("及格");
        }else {
            System.out.println("不及格");
        }



        scanner.close();
    }
}

package struct;

import java.util.Scanner;



public class Demo04 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入成绩：");
        
        int score = scanner.nextInt();
        if (score == 100){
            System.out.println("恭喜，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>=60){
            System.out.println("C");
        }else if (score<60 && score>=0){
            System.out.println("D");
        }else {
            System.out.println("输入成绩不合法");
        }




        scanner.close();
    }
}

package struct;

import java.util.Scanner;



public class Demo05 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt();
        if (a>0 && a<100){
            if (a>=50 && a<1000){
                System.out.println(a);
            }
        }else {
            System.out.println("false");
        }
        //献血案例
        int age = 22;
        int weight =70;
        if (age >= 18){
            if (weight >= 50){
                System.out.println("符合要求，可以献血");
            }
        }else {
            System.out.println("不符合要求！");
        }



        scanner.close();
    }
}