My code for the Block.java and Player.java classes are below.

Player.java:

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import javax.imageio.*;
import java.io.*;
class Player extends Entity {

    float x = Display.WINDOW_WIDTH / 2;
    float y = 430;
    float width = 48;
    float height = 103;

    float xvel = 0;
    float yvel = 0;
    float gravity = 0.4f;

    float xvel_max = 2;
    float yvel_max = 8;

    float xvel_min = -2;
    float yvel_min = -8;

    String dir = "left";

    float sword_offsetX = 14f;
    float sword_offsetY = 8;

    Boolean jumping = false; 
   
    Image sprite;
    Image sword_sprite;
    Image sprite_r;
    Image sprite_r_a1;
    Image sprite_r_a2;

    Image sprite_l;
    Image sprite_l_a1;
    Image sprite_l_a2;

    Image ssprite_r;
    Image ssprite_l;
    Player() {
        try {
            sprite_r = ImageIO.read(new File("img/player_r.png"));
            sprite_r_a1 = ImageIO.read(new File("img/player_r_a1.png"));
            sprite_r_a2 = ImageIO.read(new File("img/player_r_a2.png"));

            sprite_l = ImageIO.read(new File("img/player_l.png"));
            sprite_l_a1 = ImageIO.read(new File("img/player_l_a1.png"));
            sprite_l_a2 = ImageIO.read(new File("img/player_l_a2.png"));
        ssprite_r = ImageIO.read(new File("img/sword_r.png"));

            ssprite_l = ImageIO.read(new File("img/sword_l.png"));
            if (dir == "left") {
                sprite = sprite_r;
            }
            sword_sprite = ssprite_r;
        } catch(IOException e) {
            e.printStackTrace();
        }
    }
    Graphics2D g2d;
    void draw(Graphics g) {
        g2d = (Graphics2D) g;
        
        g2d.drawImage(sprite, (int) x, (int) y, null);
        g2d.drawImage(sword_sprite, (int) x + (int) sword_offsetX, (int) y + (int) sword_offsetY, null);
    }

    void update() {

        jumping = true;
        yvel += gravity;
        Display.graphics_panel.WorldX += xvel;  
        y += yvel;

        for (int i = 0; i < Display.graphics_panel.world.blocks.length; i++) {
            Display.graphics_panel.world.blocks[i].collide(this);
        }
    
        if (Display.keys[65] == 65 || Display.keys[68] == 68) {
                if (dir == "left") {
                    sprite = sprite_r;
                    sword_sprite = ssprite_r;
                    sword_offsetX = 14f;
                } else if (dir == "right") {
                    sprite = sprite_l;
                    sword_sprite = ssprite_l;
                    sword_offsetX = -62f;
                }
                if (xvel < 0) {
                    if (Display.graphics_panel.frameCount / 10 % 2 == 0) {
                        sprite = sprite_r_a1;
                    } else {
                        sprite = sprite_r_a2;
                    }
                }
                if (xvel > 0) {
                    if (Display.graphics_panel.frameCount / 10 % 2 == 0) {
                        sprite = sprite_l_a1;
                    } else {
                        sprite = sprite_l_a2;
                    }
                }
        }
        if (xvel == 0 && dir == "left") {
            sprite = sprite_r;
        }
        if (xvel == 0 && dir == "right") {
            sprite = sprite_l;
        }
        if (Display.keys[65] == 65) {
            xvel += 0.25;
            dir = "right";
        } else if (Display.keys[68] == 68) {

            xvel -= 0.25;
            dir = "left";
        } else {
            xvel = 0;
        }
    
    if (Display.keys[87] == 87 && jumping == false) {
        jumping = true;
        yvel = -8;
    }
        if (xvel > xvel_max) {
            xvel = xvel_max;
        } else if (xvel < xvel_min) {
            xvel = xvel_min;
        }
        if (yvel > yvel_max) {
            yvel = yvel_max;
        } else if (yvel < yvel_min) {
            yvel = yvel_min;
        }
    }
}

Block.java:

import java.awt.*;
import javax.imageio.ImageIO;
import java.io.*;
import java.awt.Rectangle;
class Block {
    Image block_sprite;
    Image dirt;
    int x;
    int y;
    int height;
    int width;
    int i = 0;
    public Block(int X, int Y, int Width, int Height, int block_type) {
        x = X * 32;
        y = Y * 32;
        width = Width;
        height = Height;
        try {
            dirt = ImageIO.read(new File("img/dirt.png"));
        } catch(IOException e) {
            e.printStackTrace();
        }
        if (block_type == 1) {
            block_sprite = dirt;
        }
    }
    
    void draw(Graphics g) {
        g.fillRect(x + Display.graphics_panel.WorldX, y, width, height);
    }
    void collide(Player player) {  
        Rectangle player_hb = new Rectangle((int) player.x, (int) player.y, (int) player.width, (int) player.height);
        Rectangle block_hb = new Rectangle(x + Display.graphics_panel.WorldX, y, width, height);

        if (player_hb.intersects(block_hb)) {
            Rectangle intersection = (Rectangle) player_hb.createIntersection(block_hb);  
           
            if (player.yvel > 0) {
                player.jumping = false;
                player.y -= intersection.getHeight();
            }
            if (player.yvel < 0) {
                player.yvel = 0;
                player.y += intersection.getHeight(); 
            }
            /* Execute this code ONLY if player is intersecting a block HORIZONTALLY!! */
            if (player.xvel > 0) {
                System.out.println("You shouldn't see this unless you run into a block!" + i++);
            }
            if (player.xvel < 0) {
                System.out.println("You shouldn't see this unless you run into a block!" + i--);
            }
        }
    }   
}

My code for the collide function is below, in Block.java:

    void collide(Player player) {  
        Rectangle player_hb = new Rectangle((int) player.x, (int) player.y, (int) player.width, (int) player.height);
        Rectangle block_hb = new Rectangle(x + Display.graphics_panel.WorldX, y, width, height);

        if (player_hb.intersects(block_hb)) {
            Rectangle intersection = (Rectangle) player_hb.createIntersection(block_hb);  
           
            if (player.yvel > 0) {
                player.jumping = false;
                player.y -= intersection.getHeight();
            }
            if (player.yvel < 0) {
                player.yvel = 0;
                player.y += intersection.getHeight(); 
            }
            /* Execute this code ONLY if player is intersecting a block HORIZONTALLY!! */
            if (player.xvel > 0) {
                System.out.println("You shouldn't see this unless you run into a block!" + i++);
            }
            if (player.xvel < 0) {
                System.out.println("You shouldn't see this unless you run into a block!" + i--);
            }
        }
    }