Java中构造代码块和成员变量初始化的顺序关系2之 Cannot reference a field before it is defined

本文探讨了Java中字段初始化的顺序问题,特别是在静态初始化块中访问未定义字段时会出现的错误。根据Java语言规范JLS 8.3.2.3节,成员变量必须在其使用前声明。然而,在特定情况下可以通过一些技巧绕过这一限制。

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public class Test1 {
	{
		a = 1;
		System.out.println(a);  // 错误
	}
	private int a = 2;

	public static void main(String[] args) {
		Test1 test1 = new Test1();
		System.out.println(test1.a);
	}
}

上面的代码会报出一个错误, Cannot reference a field before it is defined


http://stackoverflow.com/questions/14587910/why-can-you-access-static-field-before-it-is-defined-through-a-method-in-java

This is defined in the JLS 8.3.2.3. In particular:

The declaration of a member needs to appear textually before it is used [...] if the usage occurs in a [...] static initializer of C.

When you call cheat() you go around that rule. This is actually the 5th example in the list of the examples of that section.

Note that cheat() will return false in the static initializer block because test has not been initialised yet.


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