字节扫描仪没有正确比较，Java [重复]

Question

我正在尝试比较 switch 语句中的 Scanner 编号。 扫描仪工作正常，但没有进行应有的比较。

    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            default: gradeLevel = "Withdrawn";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;
    }

它总是默认为“撤回”

Answer 1

您应该在每种情况下都使用break。

来自switch documentation

每个 break 语句都会终止封闭的 switch 语句。控制流继续 switch 块之后的第一条语句。 break 语句是必要的，因为没有它们，switch 块中的语句就会失败：匹配 case 标签之后的所有语句都按顺序执行，无论后续 case 标签的表达式如何，直到遇到 break 语句

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        gradeLevel = "Withdrawn";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