java程序设计上机题，求答案

public class Point {

int x

int y

public Point() {

}

public Point(int x, int y) {

this.x = x

this.y = y

}

public Point(int x) {

this.x = x

this.y = x

}

public double distance() {//求当前点到原点的距离

return Math.sqrt((x * x + y * y))

}

public double distance(int x1, int y1) {//求当前点到（x1,y1）的距离

return Math.sqrt((x-x1)*(x-x1) + (y-y1) * (y-y1))

}

public double distance(Point other){

int x2 = other.x

int y2 = other.y

return Math.sqrt((x-x2)*(x-x2) + (y-y2) * (y-y2))

}

}

对几个容易错的稍微注解下，

1 D

2 C final修饰

3 B

4 B

5 C

6 B

7 C

8 C

9 B JAVA里面都是写作null的，而不是NULL

10 A: String.substring()大小写问题

11 C

12C

13A

14C

15A

16B

17C

18C

19D

20D管道流，此流一般用于多线

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