56 lines
1.4 KiB
Java
56 lines
1.4 KiB
Java
//: references/Immutable2.java
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// A companion class to modify immutable objects.
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class Mutable {
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private int data;
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public Mutable(int initVal) { data = initVal; }
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public Mutable add(int x) {
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data += x;
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return this;
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}
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public Mutable multiply(int x) {
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data *= x;
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return this;
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}
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public Immutable2 makeImmutable2() {
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return new Immutable2(data);
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}
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}
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public class Immutable2 {
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private int data;
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public Immutable2(int initVal) { data = initVal; }
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public int read() { return data; }
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public boolean nonzero() { return data != 0; }
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public Immutable2 add(int x) {
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return new Immutable2(data + x);
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}
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public Immutable2 multiply(int x) {
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return new Immutable2(data * x);
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}
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public Mutable makeMutable() {
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return new Mutable(data);
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}
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public static Immutable2 modify1(Immutable2 y) {
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Immutable2 val = y.add(12);
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val = val.multiply(3);
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val = val.add(11);
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val = val.multiply(2);
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return val;
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}
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// This produces the same result:
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public static Immutable2 modify2(Immutable2 y) {
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Mutable m = y.makeMutable();
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m.add(12).multiply(3).add(11).multiply(2);
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return m.makeImmutable2();
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}
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public static void main(String[] args) {
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Immutable2 i2 = new Immutable2(47);
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Immutable2 r1 = modify1(i2);
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Immutable2 r2 = modify2(i2);
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System.out.println("i2 = " + i2.read());
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System.out.println("r1 = " + r1.read());
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System.out.println("r2 = " + r2.read());
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}
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} ///:~
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