Mega Code Archive
Creating local copies with clone
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// : appendixa:LocalCopy.java
// Creating local copies with clone().
// From 'Thinking in Java, 3rd ed.' (c) Bruce Eckel 2002
// www.BruceEckel.com. See copyright notice in CopyRight.txt.
class MyObject implements Cloneable {
private int n;
public MyObject(int n) {
this.n = n;
}
public Object clone() {
Object o = null;
try {
o = super.clone();
} catch (CloneNotSupportedException e) {
System.err.println("MyObject can't clone");
}
return o;
}
public int getValue() {
return n;
}
public void setValue(int n) {
this.n = n;
}
public void increment() {
n++;
}
public String toString() {
return Integer.toString(n);
}
}
public class LocalCopy {
public static MyObject g(MyObject v) {
// Passing a reference, modifies outside object:
v.increment();
return v;
}
public static MyObject f(MyObject v) {
v = (MyObject) v.clone(); // Local copy
v.increment();
return v;
}
public static void main(String[] args) {
MyObject a = new MyObject(11);
MyObject b = g(a);
// Reference equivalence, not object equivalence:
System.out.println("a == b: " + (a == b) + "\na = " + a + "\nb = " + b);
MyObject c = new MyObject(47);
MyObject d = f(c);
System.out.println("c == d: " + (c == d) + "\nc = " + c + "\nd = " + d);
}
} ///:~
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