有关编程的菜鸟问题

Question

先上代码

convertView.setOnClickListener(new OnClickListener() {
    long lastClick;
    @Override
    public void onClick(View v) {
        if (System.currentTimeMillis() - lastClick <= 1000) {
        return;
        }
    lastClick = System.currentTimeMillis(); 
    }
});

这样写是编译通过的，但是如果我把long lastClick;放到onClick的里面第一行，然后再进行if来判断，就会报错要求对lastClick进行初始化,这时为什么啊？求解

Answer 1

long lastClick放在 函数外, 是对象的成员变量, 默认初始化为0.

放在函数内, 称为本地变量. JLS7, #16 里有写:

"EACH local variable (§14.4) and every blank final field (§4.12.4,
§8.3.1.2) must have a definitely assigned value when any access of its
value occurs. An access to its value consists of the simple name of
the variable (or, for a field, the simple name of the field qualified
by this) occurring anywhere in an expression except as the left-hand
operand of the simple assignment operator = (§15.26.1). For every
access of a local variable or blank final field x, x must be
definitely assigned before the access, or a compile-time error occurs"