java - 为什么这个 Java 程序没有显示错误？

Question

考虑下面的代码，

我忘了定义方法名，只是 block 中的代码。

public class Demo {

    {
    Apple ap;
    // Display price of Winesap.
    System.out.println("Winesap costs " + Apple.Winesap.getPrice()
            + " cents.\n");
    // Display all apples and prices.
    System.out.println("All apple prices:");
    for (Apple a : Apple.values())
        System.out.println(a + " costs " + a.getPrice() + " cents.");
    }

}

是不是因为java中的blocks{}定义了作用域？

A block {} defines the scope in Java. Each time you start a new block, you are creating a new scope. A scope determines what objects are visible to other parts of the program. It also determines the lifetime of these objects. Many other computer languages define 2 general category of scopes : global and local.

Answer 1

如 section 8.6 of the JLS 所述，您得到的是一个实例初始化器 .

它在创建实例时在任何构造函数的主体之前执行 - 就像字段初始值设定项一样。