使用put函数的变体处理TreeMap中的插入。 Java.util.TreeMap中有put()的两个变体,本文都将进行讨论。 1. put():它将指定的值与映射中的指定键相关联。如果已经存在 key ,则对其进行更新将导致该 key 的更新。
参数: key:The key with which the value is to be associated. value: The value to be associated with the given key. 返回值: It returns the previously associated value with this key, or null if there was no mapping for key. Exception: Not Available.
// Java code demonstrating the working
// of put()
import java.io.*;
import java.util.*;
public class Put {
public static void main(String[] args)
{
// Declaring the tree map of Integer and String
TreeMap<String, Integer> tmp = new TreeMap<String, Integer>();
// assigning the values in the tree map
// using put()
tmp.put("one", 1);
tmp.put("two", 3);
// Printing initial TreeMap
System.out.println("The initial TreeMap is:" + tmp);
// Putting value at key two
// replaces the previous value if present
int z = tmp.put("two", 2);
// checking the previous value associated with "two"
System.out.println("The previous value with two is:" + z);
// prints the complete map
System.out.println("Updated TreeMap is:" + tmp);
}
}
输出:
The initial TreeMap is:{one=1, two=3} The previous value with two is:3 Updated TreeMap is:{one=1, two=2}
2. putAll():它将所有映射从指定映射复制到给定映射,并在重复键的情况下覆盖。
参数: map: The mappings to be stored. 返回值: Not Available. Exception: NullPointerException: Thrown if specified map is null, specified map contains a null key.
// Java code to demonstrate the working
// of putAll()
import java.io.*;
import java.util.*;
public class putAll {
public static void main(String[] args)
{
// Declaring the tree maps of Integer and String
TreeMap<String, Integer> tmp1 = new TreeMap<String, Integer>();
TreeMap<String, Integer> tmp2 = new TreeMap<String, Integer>();
// assigning the values in the tree map
// using put()
tmp1.put("two", 3);
tmp1.put("one", 1);
// assigning in 2nd TreeMap
tmp2.put("three", 3);
tmp2.put("two", 2);
System.out.println("First treemap values are:" + tmp1);
// use of putAll()
// Putting 2nd map in 1st map
tmp1.putAll(tmp2);
System.out.println("Values after modifying 1st treemap:" + tmp1);
}
}
输出:
First treemap values are:{one=1, two=3} Values after modifying 1st treemap:{one=1, three=3, two=2}
异常
NullPointerException :如果Map包含空键或在putAll()中为空,则发生。
// Java code to demonstrate the Exception
// of putAll()
import java.io.*;
import java.util.*;
public class putAll {
public static void main(String[] args)
{
// Declaring the tree maps of Integer and String
TreeMap<String, Integer> tmp1 = new TreeMap<String, Integer>();
TreeMap<String, Integer> tmp2 = new TreeMap<String, Integer>();
// assigning the values in the tree map
// using put()
tmp1.put("two", 3);
tmp1.put("one", 1);
// assigning in 2nd TreeMap
tmp2.put("three", 3);
tmp2.put(null, 2);
System.out.println("First treemap values are:" + tmp1);
// use of putAll()
// Putting 2nd map in 1st map
tmp1.putAll(tmp2);
System.out.println("Values after modifying 1st treemap:" + tmp1);
}
}
运行时错误:
Exception in thread "main" java.lang.NullPointerException at java.util.TreeMap.put(TreeMap.java:563) at putAll.main(putAll.java:21)
实际应用:该函数具有存储值并在需要时更新它们的函数。这种函数主要在目录和词典或记录中有用。下面的一小段代码说明了合并数据库以获取游戏中的最新分数。
// Java code to demonstrate the Application
// of putAll()
import java.io.*;
import java.util.*;
public class putAllAppli {
public static void main(String[] args)
{
// Declaring the tree maps of Integer and String
TreeMap<String, Integer> Score1 = new TreeMap<String, Integer>();
TreeMap<String, Integer> Score2 = new TreeMap<String, Integer>();
// Assigning Scores at Drinks break
Score1.put("Sachin", 40);
Score1.put("Rahul", 32);
Score1.put("Dhoni", 68);
System.out.println("The scores till Drinks break are:" + Score1);
// Assigning Scores at Lunch
Score2.put("Rahul", 67);
Score2.put("Dhoni", 102);
Score2.put("Raina", 10);
System.out.println("The scores at Lunch:" + Score2);
// use of putAll()
// Getting net score board
Score1.putAll(Score2);
System.out.println("Net scorecard is:" + Score1);
}
}
输出:
The scores till Drinks break are:{Dhoni=68, Rahul=32, Sachin=40} The scores at Lunch:{Dhoni=102, Rahul=67, Raina=10} Net scorecard is:{Dhoni=102, Rahul=67, Raina=10, Sachin=40}
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注:本文由纯净天空筛选整理自Shambhavi Singh 1大神的英文原创作品 Java.util.TreeMap.put() and putAll() in Java。非经特殊声明,原始代码版权归原作者所有,本译文未经允许或授权,请勿转载或复制。