编辑代码

public class StringMethodsExample{
    public static void main(String[] args){
        String S1="Hello";
        String S2="WORD";
        String S3="Java";
        String upperCaseStr1=S1.toUpperCase();
        System.out.println("Uppercase:"+upperCaseStr1);

        String lowerCaseStr2=S2.toLowerCase();
        System.out.println("Lowercase:"+lowerCaseStr2);

        String concatStr3=S2.concat(S3);
        System.out.println("Concatenated:"+concatStr3);
    }
}