常用类02/String常用方法⭐-蒲公英云

常用类02/String常用方法⭐

String常用方法1

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String常用方法2

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String常用方法3

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注：indexof和LastIndexOf方法如果未找到都是返回-1

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

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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

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

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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
    }
}