58 lines
1.4 KiB
Java
58 lines
1.4 KiB
Java
// references/LocalCopy.java
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// (c)2016 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://mindviewinc.com/Books/OnJava/ for more book information.
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// Creating local copies with clone().
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class MyObject implements Cloneable {
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private int n;
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public MyObject(int n) { this.n = n; }
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@Override
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public Object clone() {
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Object o = null;
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try {
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o = super.clone();
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} catch(CloneNotSupportedException e) {
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System.err.println("MyObject can't clone");
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}
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return o;
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}
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public int getValue() { return n; }
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public void setValue(int n) { this.n = n; }
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public void increment() { n++; }
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@Override
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public String toString() { return Integer.toString(n); }
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}
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public class LocalCopy {
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public static MyObject g(MyObject v) {
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// Passing a reference, modifies outside object:
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v.increment();
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return v;
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}
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public static MyObject f(MyObject v) {
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v = (MyObject)v.clone(); // Local copy
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v.increment();
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return v;
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}
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public static void main(String[] args) {
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MyObject a = new MyObject(11);
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MyObject b = g(a);
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// Reference equivalence, not object equivalence:
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System.out.println("a == b: " + (a == b) +
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"\na = " + a + "\nb = " + b);
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MyObject c = new MyObject(47);
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MyObject d = f(c);
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System.out.println("c == d: " + (c == d) +
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"\nc = " + c + "\nd = " + d);
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}
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}
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/* Output:
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a == b: true
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a = 12
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b = 12
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c == d: false
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c = 47
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d = 48
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*/
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