java - 类的公共(public)成员如何在 Java 中造成严重破坏？

Question

类的公共(public)成员如何在 java 中造成严重破坏？有人可以举例说明吗？我试图创造这样的情况，但没有成功。我只是发现它们等同于“ protected ”访问修饰符。

Answer 1

它允许无效值，破坏封装。

public class Clock {
    public int hours;
    public int minutes;
}

然后，在不相关的代码中...

Clock clock = new Clock();
clock.hours = 42;
clock.minutes = 99;

使用 setter 和 getter 方法将它们设为私有(private)允许封装以强制执行正确的值。

public class Clock {
    private int hours;
    private int minutes;
    public void setHours(int hours) {
        if (hours < 0 || hours > 23) throw new IllegalArgumentException("bad range");
        this.hours = hours;
    }
    // Likewise for "setMinutes" method.
}

这是一个 tutorial page on encapsulation in Java关于封装的好处。引用:

• The fields of a class can be made read-only or write-only.

• A class can have total control over what is stored in its fields.

• The users of a class do not know how the class stores its data. A class can change the data type of a field, and users of the class do not need to change any of their code.