如何判断类在需要时才加载？

   JVM是动态加载，这点同某些静态加载语言不同，但如何证明是动态加载呢？或者说需要时才加载：

 

//: typeinfo/SweetShop.java
// Examination of the way the class loader works.
class Candy {
	static {
		System.out.println("Loading Candy");
	}
}

class Gum {
	static {
		System.out.println("Loading Gum");
	}
}

class Cookie {
	static {
		System.out.println("Loading Cookie");
	}
}

public class SweetShop {
	public static void main(String[] args) {
		System.out.println("inside main");
		new Candy();
		System.out.println("After creating Candy");
		try {
			Class.forName("Gum");
		} catch (ClassNotFoundException e) {
			System.out.println("Couldn’t find Gum");
		}
		System.out.println("After Class.forName(\"Gum\")");
		new Cookie();
		System.out.println("After creating Cookie");
	}
} 
/*
 * Output: inside main Loading Candy After creating Candy Loading Gum After
 * Class.forName("Gum") Loading Cookie After creating Cookie
 */// :~

 

静态初始化块是在类被加载时才会执行，由此证明类对象是在需要时才被加载。

 

You can see from the output that each Class object is loaded only when it’s needed, and the static initialization is performed upon class loading.