Effective Java 英文 第二版 讀書筆記 Item 14:In public classes,use accessor methods,not public fields...

本章主要分析　公開屬性與私有屬性提供公開get、set方法兩種方式對比

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// Degenerate classes like this should not be public!
class Point {
public double x;
public double y;
}

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// Public class with exposed immutable fields - questionable
public final class Time {
private static final int HOURS_PER_DAY = 24;
private static final int MINUTES_PER_HOUR = 60;
public final int hour;
public final int minute;
public Time(int hour, int minute) {
if (hour < 0 || hour >= HOURS_PER_DAY)
throw new IllegalArgumentException("Hour: " + hour);
if (minute < 0 || minute >= MINUTES_PER_HOUR)
throw new IllegalArgumentException("Min: " + minute);
this.hour = hour;
this.minute = minute;
}
... // Remainder omitted
}

Certainly, the hard-liners are correct when it comes to public classes:

if a class?is accessible outside its package, provide accessor methods, to preserve the

flexibility to change the class’s internal representation. If a public class exposes its
data fields, all hope of changing its representation is lost, as client code can be distributed
far and wide.

如果我們直接公開域，我們將無法對屬性進行限制，這樣會導致，在調用該處的代碼都要添加上限制，而修改次數隨著調用的次數而增加，

如果我們提供get，set方法，就能容易的在set方法內對傳入參數進行限制。