OnJava8-Examples/references/LocalCopy.java

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// references/LocalCopy.java
// (c)2021 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Creating local copies with clone()
class Duplo implements Cloneable {
private int n;
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Duplo(int n) { this.n = n; }
@Override public Duplo clone() { // [1]
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try {
return (Duplo)super.clone();
} catch(CloneNotSupportedException e) {
throw new RuntimeException(e);
}
}
public int getValue() { return n; }
public void setValue(int n) { this.n = n; }
public void increment() { n++; }
@Override public String toString() {
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return Integer.toString(n);
}
}
public class LocalCopy {
public static Duplo g(Duplo v) {
// Passing a reference, modifies outside object:
v.increment();
return v;
}
public static Duplo f(Duplo v) {
v = v.clone(); // Local copy // [2]
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v.increment();
return v;
}
public static void main(String[] args) {
Duplo a = new Duplo(11);
Duplo b = g(a);
// Reference equivalence, not object equivalence:
System.out.println("a == b: " + (a == b) +
"\na = " + a + "\nb = " + b);
Duplo c = new Duplo(47);
Duplo d = f(c);
System.out.println("c == d: " + (c == d) +
"\nc = " + c + "\nd = " + d);
}
}
/* Output:
a == b: true
a = 12
b = 12
c == d: false
c = 47
d = 48
*/