java学习笔记【二】之字符串常见处理方法

public class test {

public static void main(String[] args)

{

System.out.println("I ");

System.out.println("Love ");

System.out.println("China ");

}

}

输出结果：

D:\eclipse\jdk\bin\java.exe -Didea.launcher.port=53568 "-Didea.launcher.bin.path=D:\java_idea\IntelliJ IDEA 2019.1\bin" -Dfile.encoding=UTF-8 -classpath "D:\java_idea\out\production\java_idea_source;D:\java_idea\IntelliJ IDEA 2019.1\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMainV2 test

I

Love

China

Process finished with exit code 0

public class test {

public static void main(String[] args)

{

System.out.print("I ");

System.out.print("Love ");

System.out.print("China ");

}

}

输出结果：

D:\eclipse\jdk\bin\java.exe -Didea.launcher.port=53589 "-Didea.launcher.bin.path=D:\java_idea\IntelliJ IDEA 2019.1\bin" -Df ile.encoding=UTF-8 -classpath "D:\java_idea\out\production\java_idea_source;D:\java_idea\IntelliJ IDEA 2019.1\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMainV2 test

I Love China

Process finished with exit code 0

4 . 为了显示双引号,java创建一个特殊编码"，可放到字符串中，字符串中遇到改编码，将其替换成双引号。

public class test {

public static void main(String[] args)

{

System.out.println("I Love "china"");

}

}

D:\eclipse\jdk\bin\java.exe -Didea.launcher.port=53709 "-Didea.launcher.bin.path=D:\java_idea\IntelliJ IDEA 2019.1\bin" -Dfile.encoding=UTF-8 -classpath "D:\java_idea\out\production\java_idea_source;D:\java_idea\IntelliJ IDEA 2019.1\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMainV2 test

I Love "china"

Process finished with exit code 0

5. 字符串的拼接

可以使用加号“+”

public class test {

public static void main(String[] args)

{

String a="I Love ";

String b="China";

System.out.println(a+b);

}

}

输出结果：

D:\eclipse\jdk\bin\java.exe -Didea.launcher.port=54246 "-Didea.launcher.bin.path=D:\java_idea\IntelliJ IDEA 2019.1\bin" -Dfile.encoding=UTF-8 -classpath "D:\java_idea\out\production\java_idea_source;D:\java_idea\IntelliJ IDEA 2019.1\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMainV2 test

I Love China

Process finished with exit code 0

“+”还可以将字符串与变量连接起来

代码：

public class test {

public static void main(String[] args)

{

int c=2020;

String a=" I Love ";

String b="China";

System.out.println(c+a+b);

}

}

输出结果：

D:\eclipse\jdk\bin\java.exe -Didea.launcher.port=54369 "-Didea.launcher.bin.path=D:\java_idea\IntelliJ IDEA 2019.1\bin" -Dfile.encoding=UTF-8 -classpath "D:\java_idea\out\production\java_idea_source;D:\java_idea\IntelliJ IDEA 2019.1\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMainV2 test

2020 I Love China

Process finished with exit code 0

字符串的高级处理

---

1.比较两个字符串是否相等，可以使用equals（）语句； 其值返回ture或者false

代码：

public class test {

public static void main(String[] args)

{

int c=2020;

String a=" I Love ";

String b="China";

System.out.println(a.equals(b));

}

}

输出结果

D:\eclipse\jdk\bin\java.exe -Didea.launcher.port=54769 "-Didea.launcher.bin.path=D:\java_idea\IntelliJ IDEA 2019.1\bin" -Dfile.encoding=UTF-8 -classpath "D:\java_idea\out\production\java_idea_source;D:\java_idea\IntelliJ IDEA 2019.1\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMainV2 test

false

Process finished with exit code 0

2. 确定字符串长度

可以使用length（）但是其只涉及一个变量

代码：

public class test {

public static void main(String[] args)

{

int len;

String a="I Love China";

len=a.length();

System.out.println(len);

}

}

输出结果：

D:\eclipse\jdk\bin\java.exe -Didea.launcher.port=54858 "-Didea.launcher.bin.path=D:\java_idea\IntelliJ IDEA 2019.1\bin" -Dfile.encoding=UTF-8 -classpath "D:\java_idea\out\production\java_idea_source;D:\java_idea\IntelliJ IDEA 2019.1\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMainV2 test

12

Process finished with exit code 0

3.改变字符串的大小写

java提供了将字符串全部转换成大写的方法：

（toUpperCase()）

和全部转换成小写的方法：

（toLowerCase（））；

代码如下：

public class test {

public static void main(String[] args)

{

String a="I LOVE CHINA";

String b=a.toLowerCase();

System.out.println(b);

String d="fanqiuqiu i miss you";

String f=d.toUpperCase();

System.out.println(f);

}

}

输出结果：

D:\eclipse\jdk\bin\java.exe -Didea.launcher.port=55060 "-Didea.launcher.bin.path=D:\java_idea\IntelliJ IDEA 2019.1\bin" -Dfile.encoding=UTF-8 -classpath "D:\java_idea\out\production\java_idea_source;D:\java_idea\IntelliJ IDEA 2019.1\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMainV2 test

i love china

FANQIUQIU I MISS YOU

Process finished with exit code 0

4.查找字符串

要在字符串中查找，可以使用indexof() ,并将要查找到的内容放到括号之中，如果未找到字符串，返回-1，如果找到，indexof（）返回一个整数值，指出该字符串的起始位置。

代码示例：

public class test {

public static void main(String[] args)

{

String a="I LOVE CHINA ,fanqiuqiu i miss you";

String b="miss";