Example GuiContainer

package iitest.gui;

import iitest.capability.ITest;
import net.minecraft.client.gui.inventory.GuiContainer;
import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.item.ItemStack;

public class TestGui extends GuiContainer {

    ITest cap;

    public TestGui(ITest cap, EntityPlayer player) {
        super(new TestContainer(cap, player));
        this.cap = cap;
    }

    @Override
    protected void drawGuiContainerBackgroundLayer(float partialTicks, int mouseX, int mouseY) {}

    @Override
    public void drawScreen(int mouseX, int mouseY, float partialTicks) {
        super.drawScreen(mouseX, mouseY, partialTicks);
        fontRendererObj.drawString(cap.getValue() + "", 0, 0, 0xffffff);
    }
}