How to put java

Содержание

Java HashMap put()
Example 1: Java HashMap put()
Example 2: Insert Item with Duplicate Key
How to Execute an HTTP PUT Request in Java
Execute an HTTP PUT request in Java using Apache HTTP client
Execute an HTTP PUT request with headers
How to add an object in HashMap by HashMap put() method
put(K key, V value) method
putAll(Map map) method
putIfAbsent(K key, V value) method
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Java HashMap put()

Note: If key is previously associated with a null value, then also the method returns null .

Example 1: Java HashMap put()

import java.util.HashMap; class Main < public static void main(String[] args) < // create an HashMap HashMaplanguages = new HashMap<>(); // insert items to the HashMap languages.put("Java", 14); languages.put("Python", 3); languages.put("JavaScript", 1); // display the HashMap System.out.println("Programming Languages: " + languages); > >

In the above example, we have created a HashMap named languages . Here, the put() method inserts the key/value mappings to the hashmap.

Note: Every item is inserted in random positions in the HashMap .

Example 2: Insert Item with Duplicate Key

import java.util.HashMap; class Main < public static void main(String[] args) < // create an HashMap HashMapcountries = new HashMap<>(); // insert items to the HashMap countries.put("Washington", "America"); countries.put("Ottawa", "Canada"); countries.put("Kathmandu", "Nepal"); System.out.println("Countries: " + countries); // add element with duplicate key String value = countries.put("Washington", "USA"); System.out.println("Updated Countries: " + countries); // display the replaced value System.out.println("Replaced Value: " + value); > >

Countries: Updated Countries: Replaced Value: America

In the above example, we have used the put() method to insert items to the hashmap. Notice the line,

countries.put("Washington", "USA");

Here, the key Washington is already present in the hashmap. Hence, the put() method replaces the previous value America with the new value USA .

Note: Till now, we have only added a single item. However, we can also add multiple items from Map to a hashmap using the Java HashMap putAll() method.

Источник

How to Execute an HTTP PUT Request in Java

In this tutorial, you will learn how to execute an HTTP PUT request in Java. You might also be interested to learn how to execute other HTTP methods. If you are, then please check the following tutorials as well:

The HTTP PUT request method creates a new resource or replaces a representation of the target resource with the request payload. This method is Idempotent, which means that executing it should not have any side effects.

To execute an HTTP request in Java, we need to have an HTTP client as a dependency. In this tutorial, we will cover the HTTP PUT Request using the Apache HttpClient.

First, we need to add Maven dependency:

 org.apache.httpcomponents httpclient 4.5.13

Find other versions here → Apache HTTP Client. If you are not using Maven, you can also download JAR from the location above.

Execute an HTTP PUT request in Java using Apache HTTP client

Below is a simple example of executing an HTTP PUT request in Java.

import org.apache.http.HttpHeaders; import org.apache.http.HttpResponse; import org.apache.http.client.methods.HttpPut; import org.apache.http.impl.client.BasicResponseHandler; import org.apache.http.impl.client.CloseableHttpClient; import org.apache.http.impl.client.HttpClients; import java.io.IOException; public class Test < public static void main(String[] args) throws IOException < try (CloseableHttpClient httpclient = HttpClients.createDefault()) < HttpPut httpPut = new HttpPut("https://jsonplaceholder.typicode.com/posts/1"); // specify the PUT body to send to the server as part of the request httpPut.setEntity(new StringEntity("")); System.out.println("Executing PUT request. "); HttpResponse response = httpclient.execute(httpPut); System.out.println("Status code:" + response.getStatusLine().getStatusCode()); String responseBody = new BasicResponseHandler().handleResponse(response); System.out.println(responseBody); > > >

Here we used the try-with-resources to create an HttpClient. That means we don’t have to close it after executing the request. The try-with-resources statement ensures that each resource is closed at the end of the statement.

We also used the BasicResponseHandler to retrive the response body and response.getStatusLine().getStatusCode() to retrive the response status code.

Execute an HTTP PUT request with headers

We can also add HTTP headers to the request, like in the following example:

import org.apache.http.HttpHeaders; import org.apache.http.HttpResponse; import org.apache.http.client.methods.HttpUriRequest; import org.apache.http.client.methods.RequestBuilder; import org.apache.http.impl.client.BasicResponseHandler; import org.apache.http.impl.client.CloseableHttpClient; import org.apache.http.impl.client.HttpClients; import java.io.IOException; public class Test < public static void main(String[] args) throws IOException < try (CloseableHttpClient httpclient = HttpClients.createDefault()) < HttpUriRequest request = RequestBuilder.put() .setUri("https://jsonplaceholder.typicode.com/posts/1") .setHeader(HttpHeaders.CONTENT_TYPE, "application/json") .setHeader("Authorization", "Bearer 123token") // add request body .setEntity(new StringEntity("")) .build(); System.out.println("Executing PUT request. "); HttpResponse response = httpclient.execute(request); System.out.println("Status code: " + response.getStatusLine().getStatusCode()); String responseString = new BasicResponseHandler().handleResponse(response); System.out.println("Response: " + responseString); > > >

We used the RequestBuilder class to build the request with all the required data (URL, headers, request body).

Источник

How to add an object in HashMap by HashMap put() method

You have read the HashMap in Java and now we will see how to insert objects in HashMap. The HashMap class provides some methods like Java HashMap put() method, putAll() method(java map put all). Here we will discuss HashMap put example.

Here is the table content of the article will we will cover this topic.
1. put(K key, V value) method
2. putAll(Map map) method
3. putIfAbsent(K key, V value) method

put(K key, V value) method

This method is used to set the value with the corresponding key in HashMap. It inserts the entry(Key-Value) in the hashmap. If the HashMap already contained the key, then the old value is replaced by a new Value.
It returns null if there is no value presented in the hashmap for the given key. But it returns the old object if there is any value presented with the given key.

Where K is the key with which the specified value(V) is to be associated in HashMap.
V is the value to be associated with the specified key(K) in HashMap.
return NULL, if there was no mapping for key. It returns the previous value if the associated key already present.

import java.util.HashMap; public class ExampleOfHashMap < public static void main(String[] args) < HashMaphashMap = new HashMap(); // Adding element in HashMap // The put method returns the old object after performing insertion // It will return null if there is no mapping for the given key String previousObject = hashMap.put(1, "JavaGoal"); System.out.println("Previous object: "+ previousObject); // It will return the previous object and replace with a new object for given key previousObject = hashMap.put(1, "JavaGoal.com"); System.out.println("Previous object: "+ previousObject); hashMap.put(2, "Learning"); hashMap.put(3, "Website"); System.out.println("All Pair of HashMap: "+hashMap); > >

Output: Previous object: null
Previous object: JavaGoal
All Pair of HashMap:

putAll(Map map) method

This method is used to copy all elements of the specified map in the current HashMap. It copies all the mapping(Key and value pairs) of the specified Map to the current HashMap. It returns NullPointerException if the given map is null.

Where, map is specified Map which you want to copy.
return Void, it doesn’t return anything.

import java.util.HashMap; public class ExampleOfHashMap < public static void main(String[] args) < HashMaphashMap = new HashMap(); hashMap.put(1, "JavaGoal.com"); hashMap.put(2, "Learning"); hashMap.put(3, "Website"); HashMap newHashMap = new HashMap(); newHashMap.putAll(hashMap); System.out.println("All Pair of HashMap: "+newHashMap); > >

Output: All Pair of HashMap:

putIfAbsent(K key, V value) method

This method is used to put the given value with the corresponding key in HashMap. If the specified key is not already present in HashMap. It works similarly like put() method except the if condition.

Where K is the key with which the specified value(V) is to be associated with HashMap.
V is the value to be associated with the specified key(K) in HashMap.
return NULL, if there was no mapping for key. It returns the previous value if the associated key already present.

import java.util.HashMap; public class ExampleOfHashMap < public static void main(String[] args) < HashMaphashMap = new HashMap(); // Adding element in HashMap String previousObject = hashMap.putIfAbsent(1, "JavaGoal.com"); System.out.println("Previous object: "+ previousObject); hashMap.put(2, "Learning"); hashMap.put(3, "Website"); System.out.println("All Pair of HashMap: "+hashMap); > >

Output: Previous object: null
All Pair of HashMap: