JAVA基礎--常用類String

字符串相關類: String, StringBuffer

String類為不可變的字符序列

String s1="hello";
String s2="hello";
System.out.println(s1==s2); //true

s1=new String("hello");
s2=new String("hello");
System.out.println(s1==s2); //false
System.out.println(s1.equals(s2)); //true


char c[]={'s','u','n','  ', 'j','a','v','a'};
String s4=new String(c);
String s5=new String(c,4,4);
System.out.println(s4); // sun java
System.out.println(s5); //java

String類常用方法:

public class Test{
     public static void main(String[] args){
          String s1="sun java", s2="sun Java";  
          System.out.println(s1.charAt(1));  //s
          System.out.println(s1.length()); //8
          System.out.println(s1.indexOf("java")); //4
          System.out.println(s1.indexOf("Java")); //-1
          System.out.println(s1.equals(s2)); //false
          System.out.println(s1.equalsIgnoreCase(s2)); //true

           String s="我是程序員,我在學java";
            String sr=s.replace("我","你");
            System.out.println(sr); //你是程序員, 你在學java
    }  
}                

public class Test{
     public static void main(String[] args){
          String s="Welcome to Java World!";
          String s1=" sun java ";
   
          System.out.println(s.startsWith("Welcome"));  //true
          System.out.println(s.endsWith("World"));  //false
          
          String sL=s.toLowerCase();
          String sU=s.toUpperCase();
          System.out.println(sL);  // Welcome to Java World!
          System.out.println(sU);  // WELCOME TO JAVA WORLD!

          String subS=s.substring(11);
          System.out.println(subS);  // Java World!
          String sp=s1.trim();
          System.out.println(sp); //sun java
        
    }  
}           

基本數據類型包裝類:

Math類

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