Java优学网if语句入门解析：从基础语法到实战应用，轻松掌握条件判断

if (条件表达式) {

// 条件为true时执行的代码

}

int age = 18; if (age >= 18) {

System.out.println("您已成年");

}

int score = 85; boolean hasSubmitted = true;

if (score >= 60) {

if (hasSubmitted) {
    System.out.println("成绩合格，作业已提交");
} else {
    System.out.println("成绩合格，但作业未提交");
}

} else {

System.out.println("成绩不合格");

}

public boolean validateUserInput(String username, String password) {

if (username == null || username.trim().isEmpty()) {
    System.out.println("用户名不能为空");
    return false;
}

if (password == null || password.length() < 6) {
    System.out.println("密码长度至少6位");
    return false;
}

if (username.contains(" ")) {
    System.out.println("用户名不能包含空格");
    return false;
}

return true;

}

// 使用if语句处理用户权限 public void checkPermission(User user, Operation operation) {

if (user.getRole().equals("admin")) {
    executeAdminOperation(operation);
} else if (user.getRole().equals("editor")) {
    executeEditorOperation(operation);
} else if (user.getRole().equals("viewer")) {
    executeViewerOperation(operation);
} else {
    throw new PermissionDeniedException();
}

}

// 使用switch语句处理菜单选择 public void handleMenuSelection(int choice) {

switch (choice) {
    case 1:
        createNewFile();
        break;
    case 2:
        openFile();
        break;
    case 3:
        saveFile();
        break;
    case 4:
        exitProgram();
        break;
    default:
        showErrorMessage("无效选择");
}

}