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📜  Java中的提供程序 get() 方法及示例

📅  最后修改于: 2022-05-13 01:54:28.951000             🧑  作者: Mango

Java中的提供程序 get() 方法及示例

Java.security.Provider类的get()方法用于返回指定键映射到的值，如果此映射不包含该键的映射，则返回 null。

更正式地说，如果此映射包含从键 k 到值 v 的映射，满足 (key.equals(k))，则此方法返回 v；否则返回null。 （最多可以有一个这样的映射。）

句法： 

public Object get(Object key)

参数：此方法将键作为要返回其关联值的参数。

返回值：此方法返回指定键映射到的值，如果此映射不包含该键的映射，则返回 null 。

以下是说明get()方法的示例：

示例 1： 

// Java program to demonstrate
// get() method
  
import java.security.*;
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
        // Declaring int values
        int i = 10, j = 10;
  
        try {
            // creating the object of  KeyPairGenerator
            KeyPairGenerator sr = KeyPairGenerator.getInstance("DSA", "SUN");
  
            // getting the Provider of the KeyPairGenerator sr
            // by using method getProvider()
            Provider provider = sr.getProvider();
  
            // Declaring the variable of set type
            Set set;
  
            // getting unmodifiable Set view of the property entries
            set = provider.keySet();
  
            // Creating the object of iterator to iterate set
            Iterator iter = set.iterator();
  
            while (i > 0) {
  
                // getting the mapped value in element
                // using get() method
                Object element = provider.get(iter.next());
  
                // printing the mapped value
                System.out.println("value is : " + element);
                i--;
            }
        }
  
        catch (NoSuchAlgorithmException e) {
  
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出： 
value is : SHA1withDSA
value is : SHA1withDSA
value is : SHA1withDSA
value is : Software
value is : sun.security.provider.JavaKeyStore$DualFormatJKS
value is : SHA
value is : sun.security.provider.SHA
value is : sun.security.provider.JavaKeyStore$CaseExactJKS
value is : Software
value is : sun.security.provider.DSA$SHA256withDSA

示例 2： 
// Java program to demonstrate
// get() method
  
import java.security.*;
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
  
        try {
            // creating the object of  KeyPairGenerator
            KeyPairGenerator sr = KeyPairGenerator.getInstance("DSA", "SUN");
  
            // getting the Provider of the KeyPairGenerator sr
            // by using method getProvider()
            Provider provider = sr.getProvider();
  
            // getting the mapped value in element
            // using get() method
            System.out.println("Trying to get the value of an unmapped key");
            Object element = provider.get("geeks");
  
            // printing the mapped value
            System.out.println("value is : " + element);
        }
  
        catch (NoSuchAlgorithmException e) {
  
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出： 
Trying to get the value of an unmapped key
value is : null