java基础 知识—流程控制_class abc{public static void main(string args[]) {

1、分支流程控制

（1）if…else

public class HEllo {
    public static void main (String[] args){

        int a = 10,b = 20,max;
        if (a>b){
            max = a;
        }
        else {
            max = b;
        }
        System.out.println(max);
    }
}
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（2）if…else if …else
（3）switch—case

public class HEllo {
    public static void main (String[] args){
        int a = 2;
        switch (a){
            case 1:
                System.out.println("开心");
                break;
            case 2:
                System.out.println("幸福");
                break;
            default:
                System.out.println("不正确");
        }

    }
}

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2.局部变量和全局变量

public class HEllo {
    public static void main (String[] args){
        if (true){
            int b = 20;
            System.out.println(b);
        }

    }
}
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3.循环流程控制 for循环

//累加1-100
public class HEllo {
    public static void main (String[] args){
        int sum = 0;
        for (int num = 1; num <= 100;num++){
            sum += num;
        }
        System.out.println(sum);
    }
}
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break：跳出循环，continue：跳出这次循环，进行下次循环

4.字符串

public class HEllo {
    public static void main (String[] args){
        String str = "hello";
        System.out.println(str);
        //字符串拼接+
        str = "he"+"llo"+123;
        System.out.println(str);//hello123
         //如果需要读取一个字符
        String strr = "hello";
        char c = strr.charAt(0);
        System.out.println(c);
    }
}

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5.在控制台输入内容

//如果需要控制台输入，需添加此句话；
import java.util.*;
public class HEllo {
    public static void main (String[] args){
        //在控制台输入内容
        Scanner scanner = new Scanner(System.in);
        //读取在控制台输入的内容，并给line进行赋值。
        String line = scanner.nextLine();
        System.out.println(line);
        int num = scanner.nextInt();
        System.out.println(num);
//        scanner.nextDouble();
//        scanner.nextFloat();
//        scanner.nextBoolean();

       
    }
}

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6.while / do…while

public class HEllo {
    public static void main (String[] args){
        int sum = 0,num = 1;
        while (num <= 100){
            sum += num++;
        }
        System.out.println(sum);
    }
}

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