Java 中的提供程序 get()方法，示例
原文:https://www . geesforgeks . org/provider-get-method-in-Java-with-examples/
java.security.Provider 类的 get() 方法用于返回指定键映射到的值，如果该映射不包含该键的映射，则返回 null。
更正式地说，如果这个映射包含从键 k 到值 v 的映射，使得(key.equals(k))，那么这个方法返回 v；否则返回 null。(这样的映射最多只能有一个。)
语法:
public Object get(Object key)
参数:该方法将键作为要返回其关联值的参数。
返回值:该方法返回指定键映射到的值，如果该映射不包含键映射，则返回空值。
以下是举例说明 get() 方法的例子:
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<Map> type
Set<Object> 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);
}
}
}
Output:
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
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);
}
}
}
Output:
Trying to get the value of an unmapped key
value is : null
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