java流程控制：break和continue的使用

流程控制

break

终止、跳出switch、循环结构

package myFirstJava.java.测试;
public class TestBreak {
    public static void main(String[] args) {
        for (int i = 1; i <= 10; i++){
            if (i == 5){
                break;//退出整个循环结构
            }
            System.out.println("当前循环次数："+i);
        }
        System.out.println("循环结束");
    }
}

continue

结束本次，进入下一次循环

package myFirstJava.java.测试;
public class TestContinue {
    public static void main(String[] args) {
        for (int i = 1; i <= 10; i++){
            if (i == 5){
                continue;//跳过此次，进入下一次循环
            }
            System.out.println("当前循环次数："+i);
        }
        System.out.println("循环结束");
    }
}

场景项目

【成绩输入】continue

continue

依次录入五名学生的成绩，要求如果信息输入不合法则重新输入该条成绩，最后输出五名学生的平均成绩

package myFirstJava.java.测试;
import java.util.Scanner;
public class AverageScore {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        double sum = 0D;
        for(int i= 1; i <= 5; i++){
            System.out.println("请输入第"+  i +"位学生的成绩：");
            double score = input.nextDouble();
            if(score < 0 || score > 100){
				System.out.println("您的输入有误，请重新输入该学生的成绩");
                i -= 1;//本次不计数
                continue;//结束本次循环，进入下一次循环
            }
            sum += score;
        }
        double avg = sum / 5;
        System.out.println("平均分为："+avg);

代码改良

如果发现数据不合法，则此次循环不需要计数，也就是本次不需要 i++,那直接把i++写到循环最后，发现不合法输入，触发continue，本次循环中continue之后的代码都不会被执行了

double sum = 0D;
        for(int i= 1; i <= 5;){
            System.out.println("请输入第"+  i +"位学生的成绩：");
            double score = input.nextDouble();
            if(score < 0 || score > 100){
                System.out.println("您的输入有误，请重新输入该学生的成绩");
                continue;//结束循环
            }
            sum += score;
            i++;
        }

【剪刀石头布】break + continue

break,continue综合应用

人机剪刀石头布，要求三局两胜

package myFirstJava.java.测试;
import java.util.Scanner;
public class TestGuess {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int playerWin = 0;//记录人赢的次数
        int computerWin = 0;//记录机器赢的次数
        for(int i = 1; i <= 3;) {
            int computer = ((int) (Math.random() * 10)) % 3 + 1;//取随机数
            System.out.println("输入猜拳编号(1.剪刀 2.石头 3.布)");
            int player = input.nextInt();
            //比较
            if(computer == player) {
                System.out.println("平局,再来一次");
                continue;
            } else if((player == 1 && computer == 3) || (player == 2 && computer == 1) || (player == 3 && computer == 2)) {
                System.out.println("人类赢");
                playerWin ++;
                if(playerWin ==2){
                    System.out.println("人类赢两局胜出");
                    break;
                }
            } else {
                System.out.println("电脑赢");
                computerWin ++;
                if(computerWin ==2){
                    System.out.println("电脑赢两局胜出");
                    break;
                }
            }
            System.out.printf("第%d局结束
",i);
            i++;
        }
    }
}

代码改良

减少了代码冗余，减少了判断次数

		int playerWin = 0;
        int computerWin = 0;
        for(int i = 1; i <= 3;) {
            int computer = ((int) (Math.random() * 10)) % 3 + 1;
            System.out.println("输入猜拳编号(1.剪刀 2.石头 3.布)");
            int player = input.nextInt();
            if(computer == player) {
                System.out.println("平局,再来一次");
                continue;
            } else if((player == 1 && computer == 3) || (player == 2 && computer == 1) || (player == 3 && computer == 2)) {
                System.out.println("人类赢");
                playerWin +=1;
            } else {
                System.out.println("电脑赢");
                computerWin +=1;
            }
            if(computerWin == 2){
                System.out.println("电脑赢两局胜出");
                break;
            }else if(playerWin == 2){
                System.out.println("人类赢两局胜出");
                break;
            }
            System.out.printf("第%d局结束
",i);
            i++;
        }