相关疑难解决方法(0)

码:

public void placeO(int xpos, int ypos) {
    for(int i=0; i<3;i++)
        for(int j = 0;j<3;j++) {
            // The line below does not work. what can I use to replace this?
            if(position[i][j]==' ') {
                position[i][j]='0';
            }
        }
}

我想检查字符是否为空？但为什么这段代码不起作用？letterChar == null也不起作用。我用谷歌搜索了很多问题，但没有看到任何解决方案，大多数解决方案都是关于String.

String letter = enterletter.getText().toString();
char letterChar = letter.charAt(0);


if(letterChar == ' ' || letterChar == NULL) // this is where the code won't works
{
    Toast.makeText(getApplicationContext(), "Please enter a letter!", Toast.LENGTH_LONG).show();
}