In this post, we will see improved way of iterating through map and list which are introduced in java 8.
Map:
Normal way of iterating HashMap before java 8:
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package org.arpit.java2blog; import java.util.HashMap; public class HashMapIterationMap { public static void main(String args[]) { // HashMap with Country as key and capital as value HashMap<String,String> countryCapitalMap=new HashMap<String,String>(); countryCapitalMap.put("India","Delhi"); countryCapitalMap.put("Japan","Tokyo"); countryCapitalMap.put("France","Paris"); countryCapitalMap.put("Russia","Moscow"); // Iterating Using keySet() and for each loop System.out.println("Iterating Using keySet() and for each loop"); for (String countryKey:countryCapitalMap.keySet()) { System.out.println("Country:"+ countryKey +" and Capital:"+countryCapitalMap.get(countryKey)); } System.out.println("-----------------------------"); } } |
Improved way of iterating HashMap in java 8:
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package org.arpit.java2blog; import java.util.HashMap; public class HashMapIterationMap { public static void main(String args[]) { // HashMap with Country as key and capital as value HashMap<String,String> countryCapitalMap=new HashMap<String,String>(); countryCapitalMap.put("India","Delhi"); countryCapitalMap.put("Japan","Tokyo"); countryCapitalMap.put("France","Paris"); countryCapitalMap.put("Russia","Moscow"); // Iterating Using Java 8 System.out.println("Iterating Using Java 8"); System.out.println("-----------------------------"); countryCapitalMap.forEach((k,v)->System.out.println("Country:" + k + " Capital : " + v)); System.out.println("-----------------------------"); } } |
When you run above program, you will get below output:
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Iterating Using Java 8 ----------------------------- Country:Japan Capital : Tokyo Country:France Capital : Paris Country:India Capital : Delhi Country:Russia Capital : Moscow ----------------------------- |
List:
Normal way of iterating list:
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package org.arpit.java2blog; import java.util.ArrayList; public class IteratingArrayListMain { public static void main(String[] args) { ArrayList nameList=new ArrayList();//creating arraylist nameList.add("Arpit");//adding object in arraylist nameList.add("John"); nameList.add("Martin"); nameList.add("Adam"); // Iterating list using foreach loop for(String name :nameList ) { System.out.print(name+" "); } } } |
Iterating through list in java 8:
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package org.arpit.java2blog; import java.util.ArrayList; public class IteratingArrayListMain { public static void main(String[] args) { ArrayList nameList=new ArrayList();//creating arraylist nameList.add("Arpit");//adding object in arraylist nameList.add("John"); nameList.add("Martin"); nameList.add("Adam"); // Iterating list using foreach method nameList.forEach(n->System.out.print(n+" ")); } } |
forEach method internally use Consumer Object.You can read more about Java 8 Consumer interface.
When you run above program, you will get below output:
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Arpit John Martin Adam |
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