How to use the Map.Entry function in Java to perform map entry operations

The Map.Entry function in Java can be used to operate on key-value pairs in the Map, allowing us to obtain, set and delete mapping items, which is very convenient for developers who operate Maps. In this article, we will introduce in detail how to use the Map.Entry function to operate map items.

1. Overview of Map.Entry function

In Java, Map.Entry is an internal interface that allows us to access each key-value pair in the Map and operate on it. By using the Map.Entry function, we can perform get, set, and remove operations on each key-value pair in the Map, which allows us to perform flexible operations on the Map without restrictions.

2. Map.Entry function method

1. getKey() method

This method is used to obtain the key value of the key-value pair in the Map .

The sample code is as follows:

Map<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "Java");
map.put(2, "Python");
map.put(3, "JavaScript");
for (Map.Entry<Integer, String> entry : map.entrySet()) {
    System.out.println("Key: " + entry.getKey() + " Value: " + entry.getValue());
}

The output result is:

Key: 1 Value: Java
Key: 2 Value: Python
Key: 3 Value: JavaScript

2. getValue() method

This method is used to obtain the Map The value of the key-value pair in .

The sample code is as follows:

Map<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "Java");
map.put(2, "Python");
map.put(3, "JavaScript");
for (Map.Entry<Integer, String> entry : map.entrySet()) {
    System.out.println("Key: " + entry.getKey() + " Value: " + entry.getValue());
}

The output result is:

Key: 1 Value: Java
Key: 2 Value: Python
Key: 3 Value: JavaScript

3. setValue() method

This method is used to set the Map The value of the key-value pair.

The sample code is as follows:

Map<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "Java");
map.put(2, "Python");
map.put(3, "JavaScript");
for (Map.Entry<Integer, String> entry : map.entrySet()) {
    if (entry.getKey() == 2) {
        entry.setValue("Ruby");
    }
}
for (Map.Entry<Integer, String> entry : map.entrySet()) {
    System.out.println("Key: " + entry.getKey() + " Value: " + entry.getValue());
}

The output result is:

Key: 1 Value: Java
Key: 2 Value: Ruby
Key: 3 Value: JavaScript

4. equals() method

This method is used to judge two Whether the two Map.Entry objects are equal.

The sample code is as follows:

Map.Entry<Integer, String> entry1 = new AbstractMap.SimpleEntry<Integer, String>(1, "Java");
Map.Entry<Integer, String> entry2 = new AbstractMap.SimpleEntry<Integer, String>(2, "Python");
Map.Entry<Integer, String> entry3 = new AbstractMap.SimpleEntry<Integer, String>(1, "Java");
System.out.println("entry1 equals entry2? " + entry1.equals(entry2));
System.out.println("entry1 equals entry3? " + entry1.equals(entry3));

The output result is:

entry1 equals entry2? false
entry1 equals entry3? true

5. hashCode() method

This method returns Map.Entry The hash code of the object.

The sample code is as follows:

Map.Entry<Integer, String> entry1 = new AbstractMap.SimpleEntry<Integer, String>(1, "Java");
Map.Entry<Integer, String> entry2 = new AbstractMap.SimpleEntry<Integer, String>(2, "Python");
Map.Entry<Integer, String> entry3 = new AbstractMap.SimpleEntry<Integer, String>(1, "Java");
System.out.println("entry1 hashCode: " + entry1.hashCode());
System.out.println("entry2 hashCode: " + entry2.hashCode());
System.out.println("entry3 hashCode: " + entry3.hashCode());

The output result is:

entry1 hashCode: 573739522
entry2 hashCode: -931023533
entry3 hashCode: 573739522

3. Use Map.Entry to perform mapping item operations

In the method introduced above , we have learned how to get, set and delete key-value pairs in Map. Below we will use examples to demonstrate how to use the Map.Entry function to perform map entry operations.

1. Get the key-value pairs in the Map

The sample code is as follows:

Map<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "Java");
map.put(2, "Python");
map.put(3, "JavaScript");
for (Map.Entry<Integer, String> entry : map.entrySet()) {
    System.out.println("Key: " + entry.getKey() + " Value: " + entry.getValue());
}

The output result is:

Key: 1 Value: Java
Key: 2 Value: Python
Key: 3 Value: JavaScript

2. Set the key-value pairs in the Map

The sample code is as follows:

Map<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "Java");
map.put(2, "Python");
map.put(3, "JavaScript");
for (Map.Entry<Integer, String> entry : map.entrySet()) {
    if (entry.getKey() == 2) {
        entry.setValue("Ruby");
    }
}
for (Map.Entry<Integer, String> entry : map.entrySet()) {
    System.out.println("Key: " + entry.getKey() + " Value: " + entry.getValue());
}

The output result is:

Key: 1 Value: Java
Key: 2 Value: Ruby
Key: 3 Value: JavaScript

3. Delete the key-value pairs in the Map

The sample code is as follows:

Map<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "Java");
map.put(2, "Python");
map.put(3, "JavaScript");
Iterator<Map.Entry<Integer, String>> it = map.entrySet().iterator();
while (it.hasNext()) {
    Map.Entry<Integer, String> entry = it.next();
    if (entry.getKey() == 2) {
        it.remove();
    }
}
for (Map.Entry<Integer, String> entry : map.entrySet()) {
    System.out.println("Key: " + entry.getKey() + " Value: " + entry.getValue());
}

The output result is:

Key: 1 Value: Java
Key: 3 Value: JavaScript

IV. Summary

In this article, we introduced the use of Map.Entry in Java The function's method for performing map item operations. By operating on the key-value pairs in the Map, we can flexibly add, delete, modify, and query the Map, which facilitates our use of the Map in actual development. At the same time, we also provide some code examples for readers' reference. Hope this article is helpful to readers.

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