在 Java 中比较两个字符串
原文:https://www.geeksforgeeks.org/compare-two-strings-in-java/
字符串是一个字符序列。在 Java 中，String 的对象是不可变的，这意味着它们是常量，一旦创建就不能更改。
下面是用 Java 比较两个字符串的 5 种方法:
-
Using user-defined function : Define a function to compare values with following conditions :
- 如果(string1 > string2)，则返回一个正值。
- 如果两个字符串在词典上相等 (即 string1 == string2)，则返回 0 。
- if (string1 < string2) it returns a 负值。
该值计算为(int)str 1 . charat(I)–(int)str 2 . charat(I)
示例:
```java Input 1: GeeksforGeeks Input 2: Practice Output: -9
Input 1: Geeks Input 2: Geeks Output: 0
Input 1: GeeksforGeeks Input 2: Geeks Output: 8
```
程序:
```java // Java program to Compare two strings // lexicographically public class GFG {
// This method compares two strings // lexicographically without using // library functions public static int stringCompare(String str1, String str2) {
int l1 = str1.length(); int l2 = str2.length(); int lmin = Math.min(l1, l2);
for (int i = 0; i < lmin; i++) { int str1_ch = (int)str1.charAt(i); int str2_ch = (int)str2.charAt(i);
if (str1_ch != str2_ch) { return str1_ch - str2_ch; } }
// Edge case for strings like // String 1="Geeks" and String 2="Geeksforgeeks" if (l1 != l2) { return l1 - l2; }
// If none of the above conditions is true, // it implies both the strings are equal else { return 0; } }
// Driver function to test the above program public static void main(String args[]) { String string1 = new String("Geeksforgeeks"); String string2 = new String("Practice"); String string3 = new String("Geeks"); String string4 = new String("Geeks");
// Comparing for String 1 < String 2 System.out.println("Comparing " + string1 + " and " + string2 + " : " + stringCompare(string1, string2));
// Comparing for String 3 = String 4 System.out.println("Comparing " + string3 + " and " + string4 + " : " + stringCompare(string3, string4));
// Comparing for String 1 > String 4 System.out.println("Comparing " + string1 + " and " + string4 + " : " + stringCompare(string1, string4)); } } ```
Output:
```java Comparing Geeksforgeeks and Practice : -9 Comparing Geeks and Geeks : 0 Comparing Geeksforgeeks and Geeks : 8
```
-
Using String.equals() :In Java, string equals() method compares the two given strings based on the data/content of the string. If all the contents of both the strings are same then it returns true. If any character does not match, then it returns false.
语法:
java str1.equals(str2);这里，str1 和 str2 都是要比较的字符串。
示例:
```java Input 1: GeeksforGeeks Input 2: Practice Output: false
Input 1: Geeks Input 2: Geeks Output: true
Input 1: geeks Input 2: Geeks Output: false
```
程序:
```java // Java program to Compare two strings // lexicographically public class GFG { public static void main(String args[]) { String string1 = new String("Geeksforgeeks"); String string2 = new String("Practice"); String string3 = new String("Geeks"); String string4 = new String("Geeks"); String string5 = new String("geeks");
// Comparing for String 1 != String 2 System.out.println("Comparing " + string1 + " and " + string2 + " : " + string1.equals(string2));
// Comparing for String 3 = String 4 System.out.println("Comparing " + string3 + " and " + string4 + " : " + string3.equals(string4));
// Comparing for String 4 != String 5 System.out.println("Comparing " + string4 + " and " + string5 + " : " + string4.equals(string5));
// Comparing for String 1 != String 4 System.out.println("Comparing " + string1 + " and " + string4 + " : " + string1.equals(string4)); } } ```
Output:
```java Comparing Geeksforgeeks and Practice : false Comparing Geeks and Geeks : true Comparing Geeks and geeks : false Comparing Geeksforgeeks and Geeks : false
```
-
Using String.equalsIgnoreCase() : The String.equalsIgnoreCase() method compares two strings irrespective of the case (lower or upper) of the string. This method returns true if the argument is not null and the contents of both the Strings are same ignoring case, else false.
语法:
java str2.equalsIgnoreCase(str1);这里，str1 和 str2 都是要比较的字符串。
示例:
```java Input 1: GeeksforGeeks Input 2: Practice Output: false
Input 1: Geeks Input 2: Geeks Output: true
Input 1: geeks Input 2: Geeks Output: true
```
程序:
```java // Java program to Compare two strings // lexicographically public class GFG { public static void main(String args[]) { String string1 = new String("Geeksforgeeks"); String string2 = new String("Practice"); String string3 = new String("Geeks"); String string4 = new String("Geeks"); String string5 = new String("geeks");
// Comparing for String 1 != String 2 System.out.println("Comparing " + string1 + " and " + string2 + " : " + string1.equalsIgnoreCase(string2));
// Comparing for String 3 = String 4 System.out.println("Comparing " + string3 + " and " + string4 + " : " + string3.equalsIgnoreCase(string4));
// Comparing for String 4 = String 5 System.out.println("Comparing " + string4 + " and " + string5 + " : " + string4.equalsIgnoreCase(string5));
// Comparing for String 1 != String 4 System.out.println("Comparing " + string1 + " and " + string4 + " : " + string1.equalsIgnoreCase(string4)); } } ```
Output:
```java Comparing Geeksforgeeks and Practice : false Comparing Geeks and Geeks : true Comparing Geeks and geeks : true Comparing Geeksforgeeks and Geeks : false
```
-
Using Objects.equals() : Object.equals(Object a, Object b) method returns true if the arguments are equal to each other and false otherwise. Consequently, if both arguments are null, true is returned and if exactly one argument is null, false is returned. Otherwise, equality is determined by using the equals() method of the first argument.
语法:
java public static boolean equals(Object a, Object b)这里 a 和 b 都是要比较的字符串对象。
示例:
```java Input 1: GeeksforGeeks Input 2: Practice Output: false
Input 1: Geeks Input 2: Geeks Output: true
Input 1: null Input 2: null Output: true
```
程序:
```java // Java program to Compare two strings // lexicographically
import java.util.*;
public class GFG { public static void main(String args[]) { String string1 = new String("Geeksforgeeks"); String string2 = new String("Geeks"); String string3 = new String("Geeks"); String string4 = null; String string5 = null;
// Comparing for String 1 != String 2 System.out.println("Comparing " + string1 + " and " + string2 + " : " + Objects.equals(string1, string2));
// Comparing for String 2 = String 3 System.out.println("Comparing " + string2 + " and " + string3 + " : " + Objects.equals(string2, string3));
// Comparing for String 1 != String 4 System.out.println("Comparing " + string1 + " and " + string4 + " : " + Objects.equals(string1, string4));
// Comparing for String 4 = String 5 System.out.println("Comparing " + string4 + " and " + string5 + " : " + Objects.equals(string4, string5)); } } ```
Output:
```java Comparing Geeksforgeeks and Geeks : false Comparing Geeks and Geeks : true Comparing Geeksforgeeks and null : false Comparing null and null : true
```
-
语法:
java int str1.compareTo(String str2)工作: 它比较并返回如下值:
- 如果(string1 > string2)，则返回一个正值。
- 如果两个字符串在词典上相等 (即 string1 == string2)，则返回 0 。
- if (string1 < string2) it returns a 负值。
示例:
```java Input 1: GeeksforGeeks Input 2: Practice Output: -9
Input 1: Geeks Input 2: Geeks Output: 0
Input 1: GeeksforGeeks Input 2: Geeks Output: 8
```
程序:
```java // Java program to Compare two strings // lexicographically
import java.util.*;
public class GFG { public static void main(String args[]) { String string1 = new String("Geeksforgeeks"); String string2 = new String("Practice"); String string3 = new String("Geeks"); String string4 = new String("Geeks");
// Comparing for String 1 < String 2 System.out.println("Comparing " + string1 + " and " + string2 + " : " + string1.compareTo(string2));
// Comparing for String 3 = String 4 System.out.println("Comparing " + string3 + " and " + string4 + " : " + string3.compareTo(string4));
// Comparing for String 1 > String 4 System.out.println("Comparing " + string1 + " and " + string4 + " : " + string1.compareTo(string4)); } } ```
Output:
```java Comparing Geeksforgeeks and Practice : -9 Comparing Geeks and Geeks : 0 Comparing Geeksforgeeks and Geeks : 8
```
一般来说，Java 中的 equals() 和“ == ”运算符都用于比较对象以检查相等性，但以下是两者之间的一些区别:
- 之间的主要区别。equals()方法和==运算符是一个是方法，另一个是运算符。
-
One can use == operators for reference comparison (address comparison) and .equals() method for content comparison.
简单来说， ==检查两个对象是否指向同一个内存位置，反之。equals()计算对象中值的比较。
示例:
```java // Java program to understand // why to avoid == operator
public class Test { public static void main(String[] args) { String s1 = new String("HELLO"); String s2 = new String("HELLO");
System.out.println(s1 == s2);
System.out.println(s1.equals(s2)); } } ```
Output:
```java false true
```
说明:这里正在创建两个字符串对象，即 s1 和 s2。
- s1 和 s2 都指不同的对象。
- 当使用==运算符进行 s1 和 s2 比较时，结果为假，因为两者在内存中的地址不同。
- 使用 equals，结果为真，因为它只比较 s1 和 s2 中给出的值。
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