77 lines
2.4 KiB
Java
77 lines
2.4 KiB
Java
// collectiontopics/MapOps.java
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// (c)2021 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://OnJava8.com for more book information.
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// Things you can do with Maps
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import java.util.concurrent.*;
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import java.util.*;
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import onjava.*;
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public class MapOps {
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public static
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void printKeys(Map<Integer,String> map) {
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System.out.print("Size = " + map.size() + ", ");
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System.out.print("Keys: ");
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// Produce a Set of the keys:
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System.out.println(map.keySet());
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}
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public static
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void test(Map<Integer,String> map) {
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System.out.println(
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map.getClass().getSimpleName());
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map.putAll(new CountMap(25));
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// Map has 'Set' behavior for keys:
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map.putAll(new CountMap(25));
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printKeys(map);
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// Producing a Collection of the values:
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System.out.print("Values: ");
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System.out.println(map.values());
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System.out.println(map);
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System.out.println("map.containsKey(11): " +
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map.containsKey(11));
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System.out.println(
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"map.get(11): " + map.get(11));
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System.out.println("map.containsValue(\"F0\"): "
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+ map.containsValue("F0"));
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Integer key = map.keySet().iterator().next();
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System.out.println("First key in map: " + key);
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map.remove(key);
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printKeys(map);
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map.clear();
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System.out.println(
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"map.isEmpty(): " + map.isEmpty());
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map.putAll(new CountMap(25));
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// Operations on the Set change the Map:
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map.keySet().removeAll(map.keySet());
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System.out.println(
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"map.isEmpty(): " + map.isEmpty());
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}
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public static void main(String[] args) {
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test(new HashMap<>());
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test(new TreeMap<>());
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test(new LinkedHashMap<>());
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test(new IdentityHashMap<>());
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test(new ConcurrentHashMap<>());
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test(new WeakHashMap<>());
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}
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}
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/* Output: (First 11 Lines)
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HashMap
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Size = 25, Keys: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,
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12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24]
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Values: [A0, B0, C0, D0, E0, F0, G0, H0, I0, J0, K0,
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L0, M0, N0, O0, P0, Q0, R0, S0, T0, U0, V0, W0, X0, Y0]
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{0=A0, 1=B0, 2=C0, 3=D0, 4=E0, 5=F0, 6=G0, 7=H0, 8=I0,
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9=J0, 10=K0, 11=L0, 12=M0, 13=N0, 14=O0, 15=P0, 16=Q0,
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17=R0, 18=S0, 19=T0, 20=U0, 21=V0, 22=W0, 23=X0, 24=Y0}
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map.containsKey(11): true
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map.get(11): L0
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map.containsValue("F0"): true
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First key in map: 0
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Size = 24, Keys: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,
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12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24]
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map.isEmpty(): true
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map.isEmpty(): true
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...
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*/
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