公共B（​​B b）{}是什么意思？

Question

我不了解这个构造函数public B（B b）

我试图了解此构造函数的功能...请帮助我..........我想知道这种类型的构造函数的功能

包TASK04;

A类{

public static int temp = 4;
public int sum;
public int y;

public A() {
    y = temp - 2;
    sum = temp + 1;
    temp -= 2;
}

public void methodA(int m, int n) {
    int x = 0;
    y = y + m + (temp++);
    x = x + 1 + n;
    sum = sum + x + y;
    System.out.println(x + " " + y + " " + sum);
}

}

B类{

public static int x;
public int y = 5;
public int temp = -5;
public int sum = 2;

public B() {
    y = temp + 3;
    sum = 3 + temp + 2;
    temp -= 2;
}

public B(B b) {
    sum = b.sum;
    x = b.x;
    b.methodB(2, 3);
}

public void methodA(int m, int n) {
    int x = 2;
    y = y + m + (temp++);
    x = x + 5 + n;
    sum = sum + x + y;
    System.out.println(x + " " + y + " " + sum);
}

public void methodB(int m, int n) {
    int y = 0;
    y = y + this.y;
    x = this.y + 2 + temp;
    methodA(x, y);
    sum = x + y + sum;
    System.out.println(x + " " + y + " " + sum);
}

}

包TASK04;

公开课测试{

public static void main(String[] args) {
    A a1 = new A();
    B b1 = new B();
    B b2 = new B(b1);
    b1.methodA(1, 2);
    b2.methodB(3, 2);

}

}