Passing Reference Data Type Arguments

public void moveCircle(Circle circle, int deltaX, int deltaY) {
    // code to move origin of circle to x+deltaX, y+deltaY
    circle.setX(circle.getX() + deltaX);
    circle.setY(circle.getY() + deltaY);

    // code to assign a new reference to circle
    circle = new Circle(0, 0);
}

https://docs.oracle.com/javase/tutorial/java/javaOO/arguments.html

方法内部不能通过修改引用的值来改变这个引用对象；