HashMap方法之Map.getOrDefault()怎么使用

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HashMap方法 Map.getOrDefault()解读

HashMap getOrDefault(key, defaultValue) method in Java with Examples

The getOrDefault(Object key, V defaultValue) method of Map interface, implemented by HashMap class is used to get the value mapped with specified key. If no value is mapped with the provided key then the default value is returned.

Syntax:

default V getOrDefault(Object key, V defaultValue)

Parameters: This method accepts two parameters:

• key: which is the key of the element whose value has to be obtained.

• defaultValue: which is the default value that has to be returned, if no value is mapped with the specified key.

Return Value: This method returns value mapped with the specified key, otherwise default value is returned.

解释

意思就是当Map集合中有这个key时，就使用这个key值，如果没有就使用默认值defaultValue

实例

Program 1：

// Java program to demonstrate 
// getOrDefault(Object key, V defaultValue) method 

import java.util.*; 

public class GFG { 

    // Main method 
    public static void main(String[] args) 
    { 

        // Create a HashMap and add some values 
        HashMap<String, Integer> map 
            = new HashMap<>(); 
        map.put("a", 100); 
        map.put("b", 200); 
        map.put("c", 300); 
        map.put("d", 400); 

        // print map details 
        System.out.println("HashMap: "
                        + map.toString()); 

        // provide key whose value has to be obtained 
        // and default value for the key. Store the 
        // return value in k 
        int k = map.getOrDefault("b", 500); 

        // print the value of k returned by 
        // getOrDefault(Object key, V defaultValue) method 
        System.out.println("Returned Value: " + k); 
    } 
}

Output：

HashMap: {a=100, b=200, c=300, d=400}
Returned Value: 200

Program 2：

// Java program to demonstrate 
// getOrDefault(Object key, V defaultValue) method 

import java.util.*; 

public class GFG { 

    // Main method 
    public static void main(String[] args) 
    { 

        // Create a HashMap and add some values 
        HashMap<String, Integer> map 
            = new HashMap<>(); 
        map.put("a", 100); 
        map.put("b", 200); 
        map.put("c", 300); 
        map.put("d", 400); 

        // print map details 
        System.out.println("HashMap: "
                        + map.toString()); 

        // provide key whose value has to be obtained 
        // and default value for the key. Store the 
        // return value in k 
        int k = map.getOrDefault("y", 500); 

        // print the value of k returned by 
        // getOrDefault(Object key, V defaultValue) method 
        System.out.println("Returned Value: " + k); 
    } 
}

Output:

HashMap: {a=100, b=200, c=300, d=400}
Returned Value: 500

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