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May 21

[Java] static練習題

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有繼承和沒繼承StaticSuper，以下兩者有微妙的不同。

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class StaticSuper {
	static {
		System.out.println("super static block");
	}
	StaticSuper(){
		System.out.println("super constructor");
	}
}
 
public class StaticTest extends StaticSuper {
	// {
	static int rand;
 
	static {
		rand = (int) (Math.random()*6);
		System.out.println("static block " + rand);
	}
 
	StaticTest(){
		System.out.println("constructor");
	}
 
	public static void main(String[] args) {
		System.out.println("in main");
		StaticTest st = new StaticTest();
	}
}

result:

super static block
static block 5
in main
super constructor
constructor

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class StaticSuper {
	static {
		System.out.println("super static block");
	}
	StaticSuper(){
		System.out.println("super constructor");
	}
}
 
public class StaticTest {	//註解掉 extends StaticSuper
	static int rand;
 
	static {
		rand = (int) (Math.random()*6);
		System.out.println("static block " + rand);
	}
 
	StaticTest(){
		System.out.println("constructor");
	}
 
	public static void main(String[] args) {
		System.out.println("in main");
		StaticTest st = new StaticTest();
	}
}

result:

static block 1
in main
constructor

ref: Head First Java 第十章練習題

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