71 lines
1.5 KiB
Java
71 lines
1.5 KiB
Java
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// streams/OptionalMap.java
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import java.util.*;
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import java.util.stream.*;
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import java.util.function.*;
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class OptionalMap {
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static String[] elements = { "12", "", "23", "45" };
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static Stream<String> testStream() {
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return Arrays.stream(elements);
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}
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static void
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test(String descr, Function<String, String> func) {
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System.out.println(" ---( " + descr + " )---");
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for(int i = 0; i <= elements.length; i++) {
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System.out.println(
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testStream()
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.skip(i)
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.findFirst() // Produces an Optional
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.map(func));
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}
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}
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public static void main(String[] args) {
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// If Optional is not empty, map() first extracts
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// the contents which it then passes to the function:
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test("Add brackets", s -> "[" + s + "]");
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test("Increment", s -> {
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try {
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return Integer.parseInt(s) + 1 + "";
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} catch(NumberFormatException e) {
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return s;
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}
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});
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test("Replace", s -> s.replace("2", "9"));
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test("Take last digit", s -> s.length() > 0 ?
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s.charAt(s.length() - 1) + "" : s);
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}
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// After the function is finished, map() wraps the
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// result in an Optional before returning it:
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}
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/* Output:
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---( Add brackets )---
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Optional[[12]]
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Optional[[]]
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Optional[[23]]
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Optional[[45]]
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Optional.empty
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---( Increment )---
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Optional[13]
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Optional[]
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Optional[24]
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Optional[46]
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Optional.empty
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---( Replace )---
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Optional[19]
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Optional[]
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Optional[93]
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Optional[45]
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Optional.empty
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---( Take last digit )---
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Optional[2]
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Optional[]
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Optional[3]
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Optional[5]
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Optional.empty
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*/
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