在Java迭代字符串的字符

给定长度为N 的字符串str ，任务是遍历字符串并打印给定字符串的所有字符。

插图：

Input  : “GeeksforGeeks”
Output : G e e k s f o r G e e k s

Input. : “Coder”
Output : C o d e r

方法：

1. 使用朴素的方法
2. 使用 String.toCharArray() 方法
3. 使用 CharacterIterator
4. 使用 StringTokenizer
5. 使用 String.split() 方法
6. 使用番石榴库
7. 使用 String.chars() 方法
8. 使用代码点

方法 1：朴素的方法

解决这个问题的最简单方法是在[0, N – 1]范围内迭代一个循环，其中N表示字符串的长度，使用变量i并打印str[i]的值。

例子

Java

// Java Program to Iterate Over the Characters of a String
// Using Naive Approach
 
// Importing classes from respective packages
import java.io.*;
import java.util.*;
 
// Main class
class GFG {
 
    // Method 1
    // Function to traverse the string and
    // print the characters of the string
    static void traverseString(String str)
    {
        // Traverse the string
        for (int i = 0; i < str.length(); i++) {
 
            // Print current character
            System.out.print(str.charAt(i) + " ");
        }
    }
 
    // Method 2
    // Main driver method
    public static void main(String[] args)
    {
        // Custom input string
        String str = "GeeksforGeeks";
 
        // Calling the Method 1
        traverseString(str);
    }
}

输出

G e e k s f o r G e e k s 

Time Complexity: O(N)
Auxiliary Space: O(1)

方法 2：使用 String.toCharArray() 方法

在这种方法中，我们使用String.toCharArray()方法将字符串转换为字符数组。然后使用 for 循环或 for-each 循环迭代字符数组。

例子

Java

// Java Program to Iterate Over the Characters of a String
// Using String.toCharArray() method
 
// Importing classes from respective packages
import java.io.*;
import java.util.*;
 
// Main class
class GFG {
 
    // Method 1
    // To traverse the string and
    // print the characters of the string
    static void traverseString(String str)
    {
        char[] ch = str.toCharArray();
 
        // Traverse the character array
        for (int i = 0; i < ch.length; i++) {
 
            // Print current character
            System.out.print(ch[i] + " ");
        }
    }
 
    // Method 2
    // Main driver method
    public static void main(String[] args)
    {
        // Custom input string
        String str = "GeeksforGeeks";
 
        // Calling the Method 1
        traverseString(str);
    }
}

输出

G e e k s f o r G e e k s 

Time Complexity: O(N)
Auxiliary Space: O(N)

方法 3：使用 CharacterIterator

在这种方法中，我们使用 CharacterIterator 方法 current() 获取当前字符和 next() 向前移动一个位置。 StringCharacterIterator 提供了 CharacterIterator 的实现。

例子

Java

// Java Program to Iterate Over the Characters of a String
// Using CharacterIterator
 
// Importing required libraries
import java.io.*;
import java.text.*;
 
// Main class
class GFG {
 
    // Method 1
    // To traverse the string and
    // print the characters of the string
    static void traverseString(String str)
    {
        CharacterIterator it
            = new StringCharacterIterator(str);
 
        // Iterate and print current character
        while (it.current() != CharacterIterator.DONE) {
            System.out.print(it.current() + " ");
 
            // Moving onto next element in the object
            // using next() method
            it.next();
        }
    }
 
    // Method 2
    // Main driver method
    public static void main(String[] args)
    {
        // Custom input string
        String str = "GeeksforGeeks";
 
        // Calling the Method 1
        traverseString(str);
    }
}

输出

G e e k s f o r G e e k s 

Time Complexity: O(N)
Auxiliary Space: O(1)

方法 4：使用 StringTokenizer

在这种方法中，我们使用Java的StringTokenizer 类。它根据分隔符将字符串分解为标记。不鼓励使用它。

StringTokenizer(String str, String delim, boolean flag):
The first two parameters have same meaning.  The flag 
serves following purpose.

If the flag is false, delimiter characters serve to 
separate tokens. For example, if string is "hello geeks"
and delimiter is " ", then tokens are "hello" and "geeks".

If the flag is true, delimiter characters are 
considered to be tokens. For example, if string is "hello
 geeks" and delimiter is " ", then tokens are "hello", " " 
and "geeks".

例子

Java

// Java Program to Iterate Over the Characters of a String
// Using StringTokenizer
 
// Importing required librares
import java.io.*;
import java.util.*;
 
// Main class
class GFG {
 
    // Method 1
    // To traverse the string and
    // print the characters of the string
    static void traverseString(String str)
    {
        // If returnDelims is true, use the string itself as
        // a delimiter
        StringTokenizer st
            = new StringTokenizer(str, str, true);
 
        while (st.hasMoreTokens()) {
            System.out.print(st.nextToken() + " ");
        }
 
        System.out.println();
 
        // If returnDelims is false, use an empty string as
        // a delimiter
        st = new StringTokenizer(str, "", false);
 
        while (st.hasMoreTokens()) {
            System.out.print(st.nextToken() + " ");
        }
    }
 
    // Method 2
    // Main driver method
    public static void main(String[] args)
    {
        // Custom input string
        String str = "GeeksforGeeks";
 
        /// Calling the above Method1
        traverseString(str);
    }
}

输出

G e e k s f o r G e e k s 
GeeksforGeeks 

Time Complexity: O(N)
Auxiliary Space: O(N)

方法 5：使用 String.split() 方法

在这种方法中，我们使用 String 类的 split() 方法。它根据提供的正则表达式将字符串拆分为子字符串。

例子

Java

// Java Program to Iterate Over the Characters of a String
// Using String.split() method
 
// Importing required classes from respective packages
import java.io.*;
import java.util.*;
 
// Main class
class GFG {
 
    // Method 1
    // To traverse the string and
    // print the characters of the string
    static void traverseString(String str)
    {
        // Split str around matches of empty string ""
        String[] substrings = str.split("");
         
      for (String ch : substrings) {
            System.out.print(ch + " ");
        }
    }
   
    // Method 2
    // main driver method
    public static void main(String[] args)
    {
        // Custom input string
        String str = "GeeksforGeeks";
 
        // Calling the Method1 to
        // print the characters of the string
        traverseString(str);
    }
}

输出

G e e k s f o r G e e k s 

Time Complexity: O(N)
Auxiliary Space: O(N)

方法六：使用番石榴库

在这种方法中，我们使用Lists.charactersOf(str)方法，该方法返回不可变字符列表的视图。

例子

Java

// Java Program to Iterate Over the Characters of a String
// Using Guava Library
 
// Importing required classes from respective packages
import com.google.common.collect.Lists;
import java.io.*;
 
// Main class
class GFG {
 
    // Method 1
    // To traverse the string and
    // print the characters of the string
    static void traverseString(String str)
    {
        // Using enhanced for loop
        for (Character ch : Lists.charactersOf(str)) {
            System.out.print(ch + " ");
        }
 
        // A new line is required
        System.out.println();
 
        // Using listIterator on the List
        // List
        // iterator()
        // lambda
        Lists.charactersOf(str)
            .listIterator()
            .forEachRemaining(
                ch -> System.out.print(ch + " "));
 
        // A new line is required
        System.out.println();
 
        // Using method reference with listIterator
        // List
        // iterator()
        Lists.charactersOf(str)
            .listIterator()
            .forEachRemaining(System.out::print);
    }
   
    // Method 2
    // Main driver method
    public static void main(String[] args)
    {
        // Custom input string
        String str = "GeeksforGeeks";
 
        // Calling the Method1 to
        // print the characters of the string
        traverseString(str);
    }
}

输出

G e e k s f o r G e e k s 
G e e k s f o r G e e k s 
GeeksforGeeks

Time Complexity: O(N)
Auxiliary Space: O(N)

方法 7：使用 String.chars() 方法

在这种方法中，我们使用 String 类的chars()方法。由于性能原因，此方法不返回 Stream< 字符> 对象。它返回一个IntStream （整数流）对象，该对象可以转换为 Stream< 字符>（字符流）。

例子

Java

// Java Program to Iterate Over the Characters of a String
// Using String.chars() method
 
// Importing classes from required packages
import com.google.common.collect.Lists;
import java.io.*;
 
// main class
class GFG {
 
    // Method 1
    // to traverse the string and
    // print the characters of the string
    static void traverseString(String str)
    {
        // Display message for better readability
        System.out.println(
            "Auto boxing into Stream");
 
        // Using method reference
        str.chars()
            .mapToObj(Character::toChars)
            .forEach(System.out::print);
 
        str.chars().forEach(System.out::print);
 
        // A new line is required
        System.out.println();
 
        // Using lambda expressions by casting int to char
        str.chars()
            .mapToObj(i -> Character.valueOf((char)i))
            .forEach(System.out::print);
 
        // A new line is required
        System.out.println();
 
        str.chars()
            .mapToObj(i -> (char)i)
            .forEach(System.out::print);
 
        // A new line is required
        System.out.println();
        str.chars()
            .mapToObj(
                i -> new StringBuilder().appendCodePoint(i))
            .forEach(System.out::print);
 
        // A new line is required
        System.out.println();
 
        // Display message for better readability
        System.out.println(
            "Without boxing into Stream");
 
        str.chars().forEach(
            i -> System.out.print(Character.toChars(i)));
 
        // A new line is required
        System.out.println();
 
        str.chars().forEach(i -> System.out.print((char)i));
 
        // A new line is required for
        // readability in output clearly
        System.out.println();
 
        str.chars().forEach(
            i
            -> System.out.print(
                new StringBuilder().appendCodePoint(i)));
    }
 
    // Method 2
    // main driver method
    public static void main(String[] args)
    {
        // Custom input string
        String str = "GeeksforGeeks";
 
        // Calling the Method 1 to
        // print the characters of the string
        traverseString(str);
    }
}

输出

Auto boxing into Stream
GeeksforGeeks7110110110711510211111471101101107115
GeeksforGeeks
GeeksforGeeks
GeeksforGeeks
Without boxing into Stream
GeeksforGeeks
GeeksforGeeks
GeeksforGeeks

Time Complexity: O(N)
Auxiliary Space: O(N)

方法 8：使用代码点

在这种方法中，我们使用 String.codePoints() 方法返回一个 Unicode 值流。

例子

Java

// Java Program to Iterate Over the Characters of a String
// Using Code Points
 
// importing classes from respective packages
import com.google.common.collect.Lists;
import java.io.*;
 
// main class
class GFG {
 
    // Method 1
    // To traverse the string and
    // print the characters of the string
    static void traverseString(String str)
    {
        // Display message for better readability
        System.out.println(
            "Auto boxing into Stream");
       
        // Using method reference
        str.codePoints()
            .mapToObj(Character::toChars)
            .forEach(System.out::print);
        str.codePoints().forEach(System.out::print);
         
        // New kine is required
        System.out.println();
       
        // Using lambda expressions by casting int to char
        str.codePoints()
            .mapToObj(i -> Character.valueOf((char)i))
            .forEach(System.out::print);
 
        // New line is required
        System.out.println();
 
        // now using the codepoints() over the string
        str.codePoints()
            .mapToObj(i -> (char)i)
            .forEach(System.out::print);
 
        // New line is required
        System.out.println();
       
        str.codePoints()
            .mapToObj(
                i -> new StringBuilder().appendCodePoint(i))
            .forEach(System.out::print);
 
       
        System.out.println();
       
      // Display message for readability in output
      System.out.println(
            "Without boxing into Stream");
        str.codePoints().forEach(
            i -> System.out.print(Character.toChars(i)));
 
        System.out.println();
         
      str.codePoints().forEach(
            i -> System.out.print((char)i));
 
        System.out.println();
         
      str.codePoints().forEach(
            i
            -> System.out.print(
                new StringBuilder().appendCodePoint(i)));
    }
   
    // Method 2
    // main driver method
    public static void main(String[] args)
    {
        // Custom input string
        String str = "GeeksforGeeks";
 
       // Calling the Method1 to 
       // print the characters of the string
        traverseString(str);
    }
}

输出

Auto boxing into Stream
GeeksforGeeks7110110110711510211111471101101107115
GeeksforGeeks
GeeksforGeeks
GeeksforGeeks
Without boxing into Stream
GeeksforGeeks
GeeksforGeeks
GeeksforGeeks

Time Complexity: O(N)
Auxiliary Space: O(N)