Java collection map

• The Java collection map is a method to store keys and values in pairs using java language.
• It is a type of collection interface to operate data lists using their keys.
• This is also a function to collect different data, classes, and methods using key values.
• The collection map is based on the “java util” package to store, operate, and manage data list in key and value pair.
• This collection map is an interface to insert, manage, and remove values using a unique key.
• It helps to stores unique keys of value and each key of the map.
• Also, is supports inserting, store, search, and sorting the data list or value using a map key.

Syntax

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• The java collection used three maps to operate key and values.
• The category of the map is called HashMap, TreeMap, and LinkedHashMap.
• The java collection HashMap syntax is below.

Map<key - data type, key - data type> object = new HashMap<key - data type, value - data type> ();

• The java collection TreeMap syntax is below.

Map<key - data type, key - data type> object = new TreeMap<key - data type, value - data type> ();

• The java collection LinkedHashMap syntax is below.

Map<key - data type, key - data type> object = new LinkedHashMap<key - data type, value - data type> ();

• The java collection insert value in the map syntax is below.

Object.put (new data_type (key), value);

• The java collection removes value from the map syntax is below.

Object.remove (new data_type (key));

• Display the collection map syntax is below.

System.out.println(map_object);

• The iterating collection map syntax is below.

for (Map.Entry temporary_object : main_object.entrySet()){
system.out.print(temporary_object.getKey() + "-" + temporary_object.getValue()  )
}

How does the Java collection map method work?

• The key of the map must be unique and does not null.
• Import the “java. util” package for the collection map.

import java.util.*;

• Create a class with an initial capital letter and unique name.

public class JavaCollectionMap{ include variable, method, and object here… }

• Create the main class to include a collection map and get output.

public static void main(String args[]){
write java collection map code here…
}

• The write java collection map syntax here.

Map<String,String > jcm = new HashMap<String,String >();

• The insert, remove or update map value syntax use as per requirement.

jcm.put("A", "HashMap");

• The displays the output using simple syntax or iteration method.

System.out.println(jcm);

• Combine all processes and get a working procedure of the collection map.

public class JavaCollectionMap{
public static void main(String args[]){
Map<String,String > jcm = new HashMap<String,String >();
jcm.put("A", "HashMap");
jcm.put("B", "TreeMap");
jcm.put("C", "LinkedHashMap");
System.out.println(jcm);
}}

Examples

The following examples help you to understand insert, update, remove values from the collection map.

Example #1

The java collection map with insert value example and output are below.

Code:

import java.util.*;
class JavaCollectionMap{
public static void main(String args[]){
Map<Integer,String > jcm1 = new HashMap<Integer,String>();
jcm1.put (01, "HashMap");
jcm1.put (02, "TreeMap");
jcm1.put (03, "LinkedHashMap");
jcm1.put (04, "Map class");
jcm1.put (05, "Map interface");
System.out.println (jcm1);
}}

Output:

Description

• The map uses integer key and string value in the collection map.
• The “put” keyword helps to add new keys and values.

Example #2

The collection map with iteration example and output is below.

Code:

import java.util.*;
class JavaCollectionMap{
public static void main(String args[]){
Map<Integer, String > jcm1 = new HashMap<Integer, String>();
jcm1.put(01, "HashMap");
jcm1.put(02, "TreeMap");
jcm1.put(03, "LinkedHashMap");
jcm1.put(04, "Map class");
jcm1.put(05, "Map interface");
for(Map.Entry jcm:jcm1.entrySet()){
System.out.println(jcm.getKey()+" "+jcm.getValue());
}
}}

Output:

Description

• The map uses integer key and string value in the collection map.
• The “for” loop uses to iterate value from the entire list.
• The Entry and entrySet avoid the repetition of a similar algorithm.
• The “getKey()” and “getValue()” helps to display key and value in the format.

Example #3

The collection map with change value example and output is below.

Code:

import java.util.*;
class JavaCollectionMap{
public static void main(String args[]){
Map<Integer, String > jcm1 = new HashMap<Integer, String>();
jcm1.put(01, "HashMap");
jcm1.put(02, "TreeMap");
jcm1.put(03, "LinkedHashMap");
jcm1.put(04, "Map class");
jcm1.put(05, "Map interface");
System.out.println("original key and value of the Map");
for(Map.Entry jcm:jcm1.entrySet()){
System.out.println(jcm.getKey()+" "+jcm.getValue());
}
jcm1.put(new Integer(01), "Java HashMap");
jcm1.put(new Integer(02), "Java TreeMap");
jcm1.put(new Integer(03), "java LinkedHashMap");
System.out.println("Updated key and value of the Map");
for(Map.Entry jcm:jcm1.entrySet()){
System.out.println(jcm.getKey()+" "+jcm.getValue());
}
}}

Output:

Description

• The map uses integer key and string value in the collection map.
• The “put” keyword helps to add and update values.
• The key helps to change data from old to new.

Example #4

The collection map with delete value example and output is below.

Code:

import java.util.*;
class JavaCollectionMap{
public static void main(String args[]){
Map<Integer, String > jcm1 = new HashMap<Integer, String>();
jcm1.put(01, "HashMap");
jcm1.put(02, "TreeMap");
jcm1.put(03, "LinkedHashMap");
jcm1.put(04, "Map class");
jcm1.put(05, "Map interface");
System.out.println("original key and value of the Map");
for(Map.Entry jcm:jcm1.entrySet()){
System.out.println(jcm.getKey()+" "+jcm.getValue());
}
jcm1.remove(new Integer(04));
jcm1.remove(new Integer(05));
System.out.println("Deleted key and value of the Map");
for(Map.Entry jcm:jcm1.entrySet()){
System.out.println(jcm.getKey()+" "+jcm.getValue());
}
}}

Output:

Description

• The map uses integer key and string value in the collection map.
• The “remove” keyword helps to delete keys and values.
• The key helps to delete available data on the map.
• The map deletes key and value simultaneously.

Example #5

The collection map with data type’s example and output is below.

Code:

import java.util.*;
class JavaCollectionMap{
public static void main(String args[]){
Map<String, String> jcm = new HashMap<String, String>();
jcm.put ("A", "HashMap");
jcm.put ("B", "TreeMap");
jcm.put ("C", "LinkedHashMap");
System.out.println(jcm);
Map<Integer, String > jcm1 = new HashMap<Integer, String>();
jcm1.put (01, "HashMap");
jcm1.put (02, "TreeMap");
jcm1.put (03, "LinkedHashMap");
System.out.println(jcm1);
Map<Integer, Integer > jcm2 = new HashMap<Integer, Integer>();
jcm2.put (01, 71098223);
jcm2.put (02, 89901232);
jcm2.put (03, 98089921);
System.out.println(jcm2);
}}

Output:

Description

• The first map uses a string data type for key and value.
• The second map uses integer key and string value in the collection map.
• The third map uses integer data types for key and value.
• You use any data type for key and value and store data.

Conclusion

• The collection map helps to search, sort, and update data easily.
• The collection map handles the data list simply using a key.
• The map avoids repetition and complexion of the list operation.

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