整体思路：

代码设计：

代码呈现：

class Solution {
    int ret,m,n,count;
    boolean[][] vis;

    public int maxAreaOfIsland(int[][] grid) {
        m = grid.length;
        n = grid[0].length;
        vis = new boolean[m][n];

        for(int i = 0; i < m; i++)
            for(int j = 0; j < n; j++){
                if(!vis[i][j] && grid[i][j] == 1){
                    count = 0;
                    dfs(grid,i,j);
                    ret = Math.max(ret,count);
                    
                }
            }

        return ret; 
    }

    int[] dx = {0,0,1,-1};
    int[] dy = {-1,1,0,0}; 

    private void dfs(int[][] grid, int i, int j){

        count++;
        vis[i][j] = true;//使用过就标记

        for(int k = 0; k < 4; k++){
            int x = i + dx[k]; int y = j + dy[k];
            if(x >= 0 && x < m && y >= 0 && y < n && !vis[x][y] && grid[x][y] == 1){
                dfs(grid,x,y);
            }
        }
    }
}