程序首先提示:
问题:我创建了一个对象数组并在第一个if语句中填充它然后尝试在第二个if语句中访问它,我知道我不能这样做。那么我如何创建和填充对象数组并在以后访问它?有什么想法吗?
if(iUserSelection == 1) {
System.out.println();
System.out.println("How many students?");
x = oScan.nextInt();
System.out.println();
// flush the buffer
oScan.nextLine();
Student[] oClassList = new Student[x];
for(int i = 0; i < x; i++) {
System.out.println("*********************");
System.out.println("Student " + (i + 1) + " of " + x);
System.out.println("*********************");
oClassList[i] = new Student("","",0,0,0,0);
System.out.print("First Name: ");
oClassList[i].setFirstName(oScan.nextLine());
System.out.print("Last Name: ");
oClassList[i].setLastName(oScan.nextLine());
System.out.print("Homework average: ");
oClassList[i].setHWAve(oScan.nextInt());
System.out.print("Quiz average: ");
oClassList[i].setQuizAve(oScan.nextInt());
System.out.print("Project average: ");
oClassList[i].setProjectAve(oScan.nextInt());
System.out.print("Test average: ");
oClassList[i].setTestAve(oScan.nextInt());
// flush the buffer
oScan.nextLine();
System.out.println();
oClassList[i].printStudent();
}
}
if(iUserSelection == 2) {
// flush the buffer
oScan.nextLine();
if(oClassList[0] != null) {
System.out.println("Student search");
System.out.print("Enter last name: ");
sSearchLastName = oScan.nextLine();
System.out.print("Enter first name: ");
sSearchFirstName = oScan.nextLine();
}
for(int y = 0; y >= oClassList.length; y++) {
if(sSearchLastName == oClassList[y].lastName) {
System.out.println("found elements");
}
else
System.out.println("Error - Student not found");
}
}
答案 0 :(得分:1)
要在if语句退出时保持数组不被删除,请在if语句之外声明它,使其具有更宽的范围。然后,当if语句退出时,可以在if语句内填充数组,而不会超出范围。例如,
int[] arr;
if (true) {
arr = new int[1];
arr[0] = 5;
}
System.out.println(arr[0]);
输出:
5
arr将在退出if语句时保持其值,因为它在if语句之外声明,然后在内部实例化。
您更正后的代码为:
Student[] oClassList; //Declared outside of both if-statements
if(iUserSelection == 1) {
System.out.println();
System.out.println("How many students?");
x = oScan.nextInt();
System.out.println();
// flush the buffer
oScan.nextLine();
oClassList = new Student[x];
for(int i = 0; i < x; i++) {
System.out.println("*********************");
System.out.println("Student " + (i + 1) + " of " + x);
System.out.println("*********************");
oClassList[i] = new Student("","",0,0,0,0);
System.out.print("First Name: ");
oClassList[i].setFirstName(oScan.nextLine());
System.out.print("Last Name: ");
oClassList[i].setLastName(oScan.nextLine());
System.out.print("Homework average: ");
oClassList[i].setHWAve(oScan.nextInt());
System.out.print("Quiz average: ");
oClassList[i].setQuizAve(oScan.nextInt());
System.out.print("Project average: ");
oClassList[i].setProjectAve(oScan.nextInt());
System.out.print("Test average: ");
oClassList[i].setTestAve(oScan.nextInt());
// flush the buffer
oScan.nextLine();
System.out.println();
oClassList[i].printStudent();
}
}
if(iUserSelection == 2) {
// flush the buffer
oScan.nextLine();
if(oClassList[0] != null) {
System.out.println("Student search");
System.out.print("Enter last name: ");
sSearchLastName = oScan.nextLine();
System.out.print("Enter first name: ");
sSearchFirstName = oScan.nextLine();
}
for(int y = 0; y >= oClassList.length; y++) {
if(sSearchLastName == oClassList[y].lastName) {
System.out.println("found elements");
}
else
System.out.println("Error - Student not found");
}
}
答案 1 :(得分:0)
你已经知道答案了。这是一个范围问题,因此解决方案是将您的数组定义在“更宽”的范围内,您的第二个也可以看到。所以,基本上在if语句之前定义它。
答案 2 :(得分:0)
范围由块定义,块由括号{}
分隔。如果您在if
块内创建数组,则无法在其他if
块中访问该数组。
如何解决这个问题?您可以在外部块中声明数组,以便可以在所有块中访问它。
Student[] oClassList = null;
if (iUserSelection == 1) {
// ...
oClassList = new Student[x];
// ...
}
if (iUserSelection == 2) {
if(oClassList != null)
// ...
// ...
}