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Java Collections - Collections.checkedMap() Examples

[Last Updated: Dec 11, 2025]

Java Collections Java Java API 

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Class:

java.util.Collections

java.lang.Objectjava.lang.Objectjava.util.Collectionsjava.util.CollectionsLogicBig

Method:

public static <K,V> Map<K,V> checkedMap(Map<K,V> m,
                                        Class<K> keyType,
                                        Class<V> valueType)

Returns a dynamically typesafe view of the specified map.


Examples


Without using checkedMap 

package com.logicbig.example.collections;

import java.util.HashMap;
import java.util.Map;

public class CheckedMapExample {

    public static void main(String... args) {
        Map<Integer, String> map = new HashMap<>();
        map.put(1, "one");
        System.out.println(map);

        Map map2 = map;
        map2.put("two", 2);
        System.out.println(map2);
    }
}

Output

{1=one}
{1=one, two=2}
JDK 25




package com.logicbig.example.collections;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

public class CheckedMapExample2 {

    public static void main(String... args) {
        Map<Integer, String> map = new HashMap<>();
        map = Collections.checkedMap(map, Integer.class, String.class);
        map.put(1, "one");
        System.out.println(map);

        Map map2 = map;
        map2.put("two", 2);
        System.out.println(map2);
    }
}

Output

{1=one}
java.lang.ClassCastException: Attempt to insert class java.lang.String key into map with key type class java.lang.Integer
    at java.util.Collections$CheckedMap.typeCheck (Collections.java:4018)
    at java.util.Collections$CheckedMap.put (Collections.java:4064)
    at com.logicbig.example.collections.CheckedMapExample2.main (CheckedMapExample2.java:22)
    at jdk.internal.reflect.DirectMethodHandleAccessor.invoke (DirectMethodHandleAccessor.java:104)
    at java.lang.reflect.Method.invoke (Method.java:565)
    at org.codehaus.mojo.exec.AbstractExecJavaBase.executeMainMethod (AbstractExecJavaBase.java:402)
    at org.codehaus.mojo.exec.ExecJavaMojo.executeMainMethod (ExecJavaMojo.java:142)
    at org.codehaus.mojo.exec.AbstractExecJavaBase.doExecClassLoader (AbstractExecJavaBase.java:377)
    at org.codehaus.mojo.exec.AbstractExecJavaBase.lambda$execute$0 (AbstractExecJavaBase.java:287)
    at java.lang.Thread.run (Thread.java:1474)
JDK 25

See Also