java - 字节扫描仪未正确比较，Java

Question

这个问题已经有答案了:

Why do we need break after case statements? (16 个回答)

已关闭 3 年前。

我正在尝试比较 switch 语句中的扫描仪编号。扫描仪工作正常，但未按应有的方式进行比较。

    private String gradeLevel;

    public byte askGrade(){
        Scanner scan = new Scanner(System.in);
        System.out.println("Please enter grade level; ");
        System.out.println(" 1-Freshman \n 2-Sophomore \n 3-Junior \n 4-Senior ");
        byte grade = scan.nextByte();
        switch(grade){
            case 1:  gradeLevel = "Freshman";
            case 2:  gradeLevel = "Sophomore";
            case 3:  gradeLevel = "Junior";
            case 4:  gradeLevel = "Senior";
            default: gradeLevel = "Withdrawn";
        }
        return gradeLevel;
    }

始终默认为“撤回”

Answer 1

在每种情况下都应该使用 break。

来自switch documentation

Each break statement terminates the enclosing switch statement. Control flow continues with the first statement following the switch block. The break statements are necessary because without them, statements in switch blocks fall through: All statements after the matching case label are executed in sequence, regardless of the expression of subsequent case labels, until a break statement is encountered

Scanner scan = new Scanner(System.in);
System.out.println("Please enter grade level; ");
System.out.println(" 1-Freshman \n 2-Sophomore \n 3-Junior \n 4-Senior ");
byte grade = scan.nextByte();
String gradeLevel;
switch (grade) {
    case 1:
        gradeLevel = "Freshman";
        break;
    case 2:
        gradeLevel = "Sophomore";
        break;
    case 3:
        gradeLevel = "Junior";
        break;
    case 4:
        gradeLevel = "Senior";
        break;
    default:
        gradeLevel = "Withdrawn";
}
System.out.println(gradeLevel);

输出

Please enter grade level; 
 1-Freshman 
 2-Sophomore 
 3-Junior 
 4-Senior 
2
Sophomore