Java, Common substring of two string in JAVA

public String getLongestCommonSubstring(String str1, String str2)
{
            int m = str1.length();
            int n = str2.length();

            int max = 0;

            int[][] dp = new int[m][n];
            int endIndex=-1;
            for(int i=0; i<m; i++){
                for(int j=0; j<n; j++){
                    if(str1.charAt(i) == str2.charAt(j)){

                        // If first row or column
                        if(i==0 || j==0){
                            dp[i][j]=1;
                        }else{
                            // Add 1 to the diagonal value
                            dp[i][j] = dp[i-1][j-1]+1;
                        }

                        if(max < dp[i][j])
                        {
                            max = dp[i][j];
                            endIndex=i;
                        }
                    }

                }
            }
            // We want String upto endIndex, we are using endIndex+1 in substring.
            return str1.substring(endIndex-max+1,endIndex+1);
        }
    }