如何在Java中将字符串数组转换为长度数组

Question

I'm using Java 1.7 and I need to convert a String array to int array which contains length of each element in String array.

Reminder: I need to pass length array as argument of method several times and I am not interested to pass String array due to some confidential issue. Thats why I need to store lengths as int array.

For example, I have a String array something as

String[] names = {"Jack", "Bob", "Alice"};

And I need to convert it as int array of length of elements

int[] lengths = {4, 3, 5}; 

So far I tried as following but is there any built-in method or better solution?

public class ArrayLengthTest{    
     public static void main(String []args){
        String[] names = {"Jack", "Bob", "Alice"};
        int[] lengths = new int[names.length];
        for (int i = 0; i < names.length; i++) {
            lengths[i] = names[i].length();
        }
        System.out.println(java.util.Arrays.toString(lengths));// print [4, 3, 5] 
        method1(lengths);// passing length array
        method2(lengths);// passing length array
        method3(lengths);// passing length array
     }
}

Answer 1

当JDK版本为1.8或更高版本时，请尝试此操作

int[] lengths = Stream.of(names).mapToInt(String::length).toArray();

Answer 2

This is not generally required, so there is no such inbuilt methods to create a new array containing length of each string values.

The logic you mentioned is correct. you can improve the logic in case required.

If you require to use the length sometimes (not repetitive) you can directly access the length of the array element. using names[i].length(); in iteration.

If you are using JDK 1.8 then answer of saka will help.

int[] lengths = Stream.of(names).mapToInt(String::length).toArray();

but as you said you are using java 1.7 you have only option to iterate through and create array manually.

public class ArrayLengthTest{    
 public static void main(String []args){
    String[] names = {"Jack", "Bob", "Alice"};
    int[] lengths = new int[names.length];
    for (int i = 0; i < names.length; i++) {
        lengths[i] = names[i].length();
    }
    System.out.println(java.util.Arrays.toString(lengths));// print [4, 3, 5] 
    method1(lengths);// passing length array
    method2(lengths);// passing length array
    method3(lengths);// passing length array
 }
}

Answer 3

If you are declaring your string array manually as you have done above, then there is no other efficient way than what you already have, any inbuilt method you use will have the same complexity. But, if you are building the String array dynamically, then you can also build the lengths array as you assign each String to the String array.