常用类02/String常用方法⭐

左手的ㄟ右手 2023-10-04 16:41 84阅读 0赞

##### String常用方法1 #####

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70]

##### String常用方法2 #####

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 1]

##### String常用方法3 #####

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 2]

##### 注：indexof和LastIndexOf方法如果未找到都是返回-1 #####

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> **String常用方法1举例**

package com.cyl;
    
    import org.junit.Test;
    
    import java.util.Locale;
    
    public class StringMethodTest {
        
    
        @Test
        public void test(){
        
            String s1 = "Hello,World";
    
            //1. int length()
            System.out.println(s1.length());
    
            //2. char charAt(int index)
            System.out.println(s1.charAt(0));
            System.out.println(s1.charAt(10));
    
            //3. boolean isEmpty()
            s1 = "";
            System.out.println(s1.isEmpty());
    
            //4. String toLowerCase()与String toUpperCase()
            String s2 = "Hello,World";
            String s3 = s2.toLowerCase();//String toUpperCase()跟它意思相反
            System.out.println(s2);//s2不可变，仍为原来的字符串
            System.out.println(s3);//改成小写以后String s2 = "Hello,World";的字符串
    
            //5. String trim()
            String s4 = "  H   ello,  Wor  ld  ";
            String s5 = s4.trim();
            System.out.println("==="+ s4 +"===");
            System.out.println("==="+ s5 +"===");
    
            //6. boolean equals(Object obj)与boolean equalsIgnoreCase(Object obj)
            String s6 = "HelloWorld";
            String s7 = "helloworld";
            System.out.println(s6.equals(s7));
            System.out.println(s6.equalsIgnoreCase(s7));
    
            //7. String concat(String str)
            String s8 = "abc";
            String s9 = s8.concat("def");
            System.out.println(s9);
    
            //8. int compareTo(String anotherString)  涉及到字符串排序
            String s10 = "abc";
            String s11 = new String("abe");
            System.out.println(s10.compareTo(s11));//-2 。挨个比，到第三位时c小于e，说明s10小于s11
    
            //9. String substring(int beginIndex)与String substring(int beginIndex，int endIndex)
            String s12 = "java常用类";
            String s13 = s12.substring(2);
            System.out.println(s12);
            System.out.println(s13);
            String s14 = s12.substring(2,5);
            System.out.println(s14);
    
        }
    }

> 运行结果

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 3]

--------------------

> **String常用方法2举例**

package com.cyl;
    
    import org.junit.Test;
    
    import java.util.Locale;
    
    public class StringMethodTest {
        
    
        @Test
        public void test2(){
        
    
            String str1 = "helloworld";
    
            //boolean endsWith(String suffix)
            boolean b1 = str1.endsWith("ld");
            System.out.println(b1);
    
            //boolean startsWith(String prefix)
            boolean b2 = str1.startsWith("He");
            System.out.println(b2);
    
            //boolean startsWith(String prefix, int toffset)
            boolean b3 = str1.startsWith("ll",2);
            System.out.println(b3);
        }
    }

> 运行结果  
> ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 4]

package com.cyl;
    
    import org.junit.Test;
    
    import java.util.Locale;
    
    public class StringMethodTest {
        
    
        @Test
        public void test2(){
        
            String str1 = "helloworld";
            String str2 = "wo";
    
            //boolean contains(CharSequence s)
            System.out.println(str1.contains(str2));
    
            //int indexOf(String str)
            System.out.println(str1.indexOf("lo"));
            System.out.println(str1.indexOf("lox"));
    
            //int indexOf(String str, int formIndex)
            System.out.println(str1.indexOf("lo",5));
    
            //int lastIndexOf(String str)
            String str3 = "aaoraaaoraaaa";
            System.out.println(str3.lastIndexOf("or"));
    
            //int lastIndexOf(String str, int fromIndex)
            System.out.println(str3.lastIndexOf("or",4));
        }
    }

> 运行结果

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 5]

--------------------

> **String常用方法3举例**

age com.cyl;
    
    import org.junit.Test;
    
    import java.util.Locale;
    
    public class StringMethodTest {
        
    
        @Test
        public void test3(){
        
            //替换
            String str1 = "java基础知识";
            String  str2 = str1.replace('知','只');
    
            System.out.println(str1);
            System.out.println(str2);
    
            String str3 = str1.replace("基础","高阶");
            System.out.println(str3);
            //其他的替换需要涉及正则表达式，之后会单独讲
            
        }
    }

> 运行结果

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 6]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/2b520c735bf843a681df3f8b77f8e879.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/b768f555f71345c8abda3e486a7c798f.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 2]: https://img-blog.csdnimg.cn/12e65f9e37664617855dedd8156e63e9.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 3]: https://img-blog.csdnimg.cn/b489d05e91f54b82a947acb13ace2e01.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 4]: https://img-blog.csdnimg.cn/324fe62c446b4798839d245b3e6123dd.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 5]: https://img-blog.csdnimg.cn/d31af8b75a844568a4fe5bedf3690345.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA_size_16_color_FFFFFF_t_70 6]: https://img-blog.csdnimg.cn/55aa7ad4664c416e85854717514c9df1.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80ODA2MzY2MA==,size_16,color_FFFFFF,t_70