Java 中的 Java.util.TreeMap.put()和 putAll()
原文:https://www . geesforgeks . org/Java-util-tree map-put-putall-Java/
TreeMap 中的插入是使用 put 函数的变体来处理的。Java.util.TreeMap 中有两个 put()的和变体，本文将对这两个变体进行讨论。
1。put() : 它将指定值与地图中的指定键相关联。如果一个键已经存在，那么更新它会导致该键的更新。
Parameters:
key : The key with which the value is to be associated.
value : The value to be associated with the given key.
Return Value:
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的映射复制到给定的映射，并在重复按键的情况下覆盖。
Parameters:
map : The mappings to be stored.
Return Value:
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}
Exception
空指针异常:如果映射包含空键或在 putAll()中为空，则会出现该异常。
// 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:这个功能可以存储数值，如果需要可以更新。这种功能主要在目录和字典或记录中有用。下面的一个小代码解释了如何组合数据库来获得游戏中的更新分数。
// 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}
本文由 香巴拉维·辛格 供稿。如果你喜欢 GeeksforGeeks 并想投稿，你也可以使用contribute.geeksforgeeks.org写一篇文章或者把你的文章邮寄到 contribute@geeksforgeeks.org。看到你的文章出现在极客博客主页上，帮助其他极客。 如果发现任何不正确的地方，或者你想分享更多关于上述话题的信息，请写评论
版权属于：月萌API www.moonapi.com，转载请注明出处
