Java中concat()和+运算符的区别

Input: String 1 : abc
String 2 : def
String n-1 : ...
String n : xyz
Output: abcdef...xyz


// Java Program to Demonstrate Working of concat() method
// Main class
class GFG {
    // Main driver method
    public static void main(String args[])
    {
        // Custom input string 1
        String s = "Geeks ";
        // Custom input string 2 is passed as in arguments
        // Here we are adding it to end of same string
        s = s.concat("for Geeks");
        // Printing the concatenated string
        System.out.println(s);
    }
}


Geeks for Geeks


// Java Program to Demonstrate Working of + Operator
// over Strings
// Main class
class GFG {
    // Main driver method
    public static void main(String args[])
    {
        // Custom input strings
        String s1 = " Geeks ";
        String s2 = " for Geeks ";
        // Now using + operator over string where
        // flexibility is provided to add on either side
        String s3 = s1 + s2;
        String s4 = s2 + s1;
        // Printing strings formed after
        // using + operator
        System.out.println(s3);
        System.out.println(s4);
    }
}


Geeks for Geeks
for Geeks Geeks


// Java Program to Illustrate concat() method
// vs + operator in Strings
// Main class
public class GFG {
    // Main driver method
    public static void main(String[] args)
    {
        // Custom input string
        String s = "Geeks", t = "for", g = "geeks";
        // Printing combined string using + operator
        System.out.println(s + t + g);
        // Printing combined string using concat() method
        System.out.println(s.concat(t));
    }
}


Geeksforgeeks
Geeksfor


// Java Program to Illustrate Raise of NullPointer Exception
// in case of concat() Method
// Main class
public class GFG {
    // Main driver method
    public static void main(String[] args)
    {
        // Input string 1
        String s = "Geeks";
        // Input string 2
        String r = null;
        // Combining above strings using + operator and
        //  printing resultant string
        System.out.println(s + r);
        // Combining above strings using concat() method and
        // printing resultant string
        // It raises an NullPointer Exception
        System.out.println(s.concat(r));
    }
}


// Java Program to Illustrate Creation of New String object
// in concat() method and + Operator
// Main class
public class GFG {
    // Main driver method
    public static void main(String[] args)
    {
        // Input strings
        String s = "Geeks", g = "";
        // Using concat() method over strings
        String f = s.concat(g);
        // Checking if both strings are equal
        // Case 1
        if (f == s)
            // Identical strings
            System.out.println("Both are same");
        else
            // Non-identical strings
            System.out.println("not same");
        // Case 2
        String e = s + g;
        // Again checking if both strings are equal
        if (e == s)
            // Identical strings
            System.out.println("Both are same");
        else
            // Non-identical strings
            System.out.println("not same");
    }
}


Both are same
not same