Question

Creating a program for a user to input the number of push ups they did in a session, displaying that session's number in one textview while showing the sum of all push up sessions in a second textview.

I tried the code below which seemed to work for a lot of people but I am getting the error "cannot resolve symbol i"

is there an issue with my code, or this method? Any tips on finding the sum of arraylist items in a date range would be much appreciated too

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    final ArrayList<Integer> pushuplist = new ArrayList<>();

    EditText PushupEditText = findViewById(R.id.PushupEditText);
    Button AddButton = (Button) findViewById(R.id.Submit);
    AddButton.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            EditText PushupEditText = findViewById(R.id.PushupEditText);
            TextView PushupTextView = findViewById(R.id.PushupTextView);
            TextView TotalPushupsText = findViewById(R.id.TotalPushupsText);

            int PushupNum = Integer.parseInt(PushupEditText.getText().toString());
            pushuplist.add(PushupNum);

            PushupTextView.setText(PushupNum+"");

            int sum = 0;
                for (int i = 0; i < pushuplist.size(); i++);
            {
                sum += pushuplist.get(i);
            }

        }
    });

Answer 1

删除最后一个分号：

for (int i = 0; i < pushuplist.size(); i++);

Answer 2

下面的代码在for循环声明之后有一个多余的分号。删除该分号即可解决问题。

int sum = 0;
for(int i = 0; i < pushuplist.size(); i++); // remove this semicolon
{
    sum += pushuplist.get(i);
}

如果您想知道为什么它不会触发编译器错误或警告，请继续阅读。

编写for循环时，如果不添加花括号，则下一个可执行语句将在该for循环的迭代中运行。

for(int i = 0; i < 10; i++) System.out.println(i);

for(int i = 0; i < 10; i++)
    System.out.println(i);

这些都是有效代码的实例。在这两种情况下，打印都会被触发10次，并将打印出i的值。

如果for循环声明后有分号（如您的分号）：

for(int i = 0; i < pushuplist.size(); i++);

下一个可执行语句是分号;，因此在所有for循环迭代中都不会运行任何内容。

希望这种解释应能使人们对那里发生的事情有所了解。

祝您的应用程序好运！

Answer 3

您在for（）中有一个小错误请改用此代码。

protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final ArrayList<Integer> pushuplist = new ArrayList<>();

EditText PushupEditText = findViewById(R.id.PushupEditText);
Button AddButton = (Button) findViewById(R.id.Submit);
AddButton.setOnClickListener(new View.OnClickListener() {

    @Override
    public void onClick(View v) {
        EditText PushupEditText = findViewById(R.id.PushupEditText);
        TextView PushupTextView = findViewById(R.id.PushupTextView);
        TextView TotalPushupsText = findViewById(R.id.TotalPushupsText);

        int PushupNum = Integer.parseInt(PushupEditText.getText().toString());
        pushuplist.add(PushupNum);

        PushupTextView.setText(PushupNum+"");

        int sum = 0;
        for (int i = 0; i < pushuplist.size(); i++)
        {
            sum += pushuplist.get(i);
        }

    }
});

How to calculate sum of integers ArrayList from user input

3 个答案: