高级内存

引用类型 值类型化

引用类型的潜在风险

Driver.java
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public class Driver {    ...    public static void main(String[] args) {        Point point = new Point(1, 2);         Rect rect1 = new Rect();        rect1.setPoint(point);        rect1.setWidth(3);        rect1.setHeight(6);         point.setX(3);         Rect rect2 = new Rect();        rect2.setPoint(point);        rect2.setWidth(3);        rect2.setHeight(6);    }    ...}

使用一般方法拷贝对象

Point.java
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public class Point {    public Point copy() {        return new Point(x, y);    }}

Driver.java
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public class Driver {    ...    public static void main(String[] args) {        Point point = new Point(1, 2);         Rect rect1 = new Rect();        rect1.setPoint(point);        rect1.setWidth(3);        rect1.setHeight(6);         Point p2 = point.copy();         Rect rect2 = new Rect();        rect2.setPoint(p2);        rect2.setWidth(3);        rect2.setHeight(6);    }    ...}

使用拷贝构造拷贝对象

Point.java
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public class Point {    public Point(Point point) {        x = point.x;        y = point.y;    }}

Driver.java
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public class Driver {    ...    public static void main(String[] args) {        Point point = new Point(1, 2);         Rect rect1 = new Rect();        rect1.setPoint(point);        rect1.setWidth(3);        rect1.setHeight(6);         Point p2 = new Point(point);         Rect rect2 = new Rect();        rect2.setPoint(p2);        rect2.setWidth(3);        rect2.setHeight(6);    }    ...}

使用不变对象机制

只有构造方法会给属性赋值

不提供任何方法修改属性

任何看似修改对象属性的方法，均会创建一个新的对象，并返回

Point.java
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public class Point {    public Point translated(int dx, int dy) {        return new Point(x + dx, y + dy);    }}

Driver.java
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public class Driver {    ...    public static void main(String[] args) {        Point point = new Point(1, 2);         Rect rect1 = new Rect();        rect1.setPoint(point);        rect1.setWidth(3);        rect1.setHeight(6);         Point p2 = point.translated(1, 0);         Rect rect2 = new Rect();        rect2.setPoint(p2);        rect2.setWidth(3);        rect2.setHeight(6);    }    ...}