方法包含在java.lang.String中。String型別一經建立就不可改變。可變的字串可用StringBuffer型別或者StringBuilder型別。
程式碼如下：

package Stringpackage;

public class StringFunction {
    public static void main(String[] args)
    {
        String a=new String("abcdefg");
        String b=new String("Abcdefg");
        String c=new String("a bc"
 
);
        String d=new String("abcabcabcabc");
        //按字典順序比較兩個字串，返回int值,相等返回0，小於字串引數返回小於0的值，大於字串引數返回大於0的值；
        System.out.println("The result of a compare to b is "+a.compareTo(b)+"\n"+"The result of b compare to a is "+a.compareTo(c));
        System.out.println("----------------------------------"
 
);
        //按字典順序比較兩個字串，忽略大小寫；
        System.out.println("a compare to b ignoring case : "+a.compareToIgnoreCase(b));
        System.out.println("----------------------------------");
        //將字串引數連線到字串的末尾；
        System.out.println("connect b to the end of a: "+a.concat(b));
        System.out.println
 
("----------------------------------");
        // 當且僅當此字串包含指定的 char 值序列時，返回 true。
        System.out.println("tell if a contains appointed String: "+a.contains("bcd"));
        System.out.println("----------------------------------");
        // 將此字串與指定的 StringBuffer 或者charsequence比較。
        System.out.println("tell if a equals  to a StringBuffer or a charsequence: "+a.contentEquals("abcd"));
        System.out.println("----------------------------------");
        //測試該字串是否以指定字尾sffix結束 
        System.out.println("tell a is end with appointed String: "+"\n"+a.endsWith("efg")+"\n"+a.endsWith("df"));
        System.out.println("----------------------------------");
        //判斷字串是否為空
        System.out.println("tell a is empty"+a.isEmpty());
        System.out.println("----------------------------------");
        //輸出字串的長度：
        System.out.println("the length of appointed String is: "+c.length());
        System.out.println("----------------------------------");
        //用指定的子串替換字串中的特定的子串
        System.out.println("the pre d is: "+d+"\n"+"the followed d is: "+d.replace("ab", "ef"));
        System.out.println("----------------------------------");

    }
}

輸出結果為：

The result of a compare to b is 32
The result of b compare to a is 66
----------------------------------
a compare to b ignoring case : 0
----------------------------------
connect b to the end of a: abcdefgAbcdefg
----------------------------------
tell if a contains appointed String: true
----------------------------------
tell if a equals  to a StringBuffer or a charsequence: false
----------------------------------
tell a is end with appointed String: 
true
false
----------------------------------
tell a is emptyfalse
----------------------------------
the length of appointed String is: 4
----------------------------------
the pre d is: abcabcabcabc
the followed d is: efcefcefcefc
----------------------------------

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